The development trend of gears, focusing on high-speed,heavy-duty,light weight,and small sizes makes hardness promotion of gear face through traditional surface treatment and improvement of the bearing capacity of gears by enlarging module face enormous boundaries. Special work conditions require new type of surface strengthening method as well as new gear materials with high performance. To confirm the effect of surface engineering on load carrying capacity of gears, this paper dwells on load carrying capacity of gears, particularly wear resistance, frictional behavior, and mechanical properties of gear surface deposited by coating. Among the common ceramic coatings, the titanium nitride (TiN) is featured by excellent wear-resistance and low friction against to metals, making them widely used in tool and die industry. This article originates from two projects of National Natural Science Foundation of China,“the study on process and property of surface ceramic coated gears”(No.50375164) and“the study on process and load carrying capacity of ceramic coated surface gears”(50105022).By taking TiN coating as research target, theoretically and experimentally, this paper discusses process of TiN deposition on gear face and its effect on load carrying capacity, so as to provide beneficial experiences for researches on new processes of gear surface strengthening. Major work accomplished in this paper is as follows: (1) By means of contact finite element analysis, stress field and load of rig test experiment has been confirmed. Contact stress characters of gear under friction force have been analyzed in this paper. (2) Taking particularity of gear material, heat treatment and characteristic of process to prepare TiN into consideration, this paper offers technical thought of synthesis the TiN on the gear face. (3) TiN deposition process has been applied to different gear materials through optimizing process experiments, so as to determine suitable materials for TiN deposition. (4) Wear resistance, antifriction characters of TiN and its effects on substrate ductility have been researched by means of frictional wear test and impact test. (5) The effects of TiN on load carrying capacity of gear have been explored by analyzing frictional force and bending property. (6) By means of contact fatigue experiment and gear rig test, the load carrying capacity of TiN coated gears has been analyzed. Based on the theoretical and experimental analysis, frictional behavior of different nitrided steel deposited by TiN show different wear resistance, among which 32Cr2MoV is best. The friction force influences the contact stress of load bearing gears, and favorable effect of TiN on gear depends on the mechanical properties of TiN, such as higher hardness. The increased amplitude of stiffness of TiN gears is small and titanium has no influence on bending resistance. The comparison of impact ductility between nitrided 32Cr2MoV and TiN coated 32Cr2MoV reveals that temperature of TiN deposition is so low that TiN has no effect on the core ductility, while increasing the surface hardness, wear-resistance and ductility of materials. The deposition of TiN onto nitrided 32Cr2MoV increases the residual compression stress of tooth surface, which helps to improve the bonding strength of coating/substrate, thereby reduces the effects of contact load.After comparing the contact fatigue limit of nitrided and TiN coated 32Cr2MoV through line contact roller fatigue experiment and wear resistance with gearbox running test, this paper puts forward the conclusion that TiN improves contact fatigue strength, wear resistance and scratch resistance of gear face. Reaches done in this paper enriches theories and methods of gear surface strengthening, providing beneficial research fruits for application of coating process in gears. The innovations of this paper are as follows: (1) Match relation of gear material and coating process has been researched in this paper. Gear materials suitable for titanium deposition have been finalized through optimizing process experiment. Subsequently titanium deposition has been applied to those materials. The process of deposition on to the gear material is the first time to be proposed domestically. (2) Domestically, it is the first time to proceed Frictional wear test and impact test of TiN coated nitrided gears so as to investigate the effect of TiN on gear strength through analysis of friction force, bending deformation, (3) Domestically it is the first time to analyze load carrying capacity of TiN coated nitrided gears by means of contact fatigue test and gear rig test. The performances of the TiN coated gears are better.