In this paper, the property and the structure of Sialon ceramics are introduced. Simultaneously the study and application of present condition about Sialon ceramics at home and abroad are also discussed. In addition, this paper put forward the existent problem and expectation on study and application of Sialon ceramics. This subject studied the influence of different additives on the microstructure and mechanical property of Sialon ceramics systemicly. For Sialon is sosoloid of Si_3N_4-SiO_2-Al_2O_3-AlN system, some a concrete phase can be synthesized according to the mixture ratio of phase diagram and choosing appropriate conditions. Sialon ceramics have been studied by pressureless sintering with the components of Si_3N_4, Al_2O_3, AlN at 1750℃. Because of the different components, different mechanical properties and microstructure can be found in different samples. The morphologies and the mechanical properties of Sialon ceramics prepared by pressureless sintering were investigated. According to the result, the optimal composition was confirmed: the sample A3 which is composed with 56%α-Si_3N_4, 34%Al_2O_3 and 10%AlN has the relative better mechanical property and the flexure strength and the fracture toughness are up to 362.5MPa and 3.31MPam~(1/2) respectively. Choosing Y_2O_3,La_2O_3,Ce_2O_3,Nd_2O_3 and Sm_2O_3 as different fluxing agents and Sialon ceramics prepared above as parent materials, we studied the influence of the fluxing agents contents of different on the morphologies and the mechanical properties of Sialon ceramics. The microstructure were analyzed by deferent analysis methods such as X-ray Diffraction(XRD) and scanning electron microscope(SEM) and the mechanical properties were tested by three-point bending method and single edge notched beam method. Results showed that the mechanical property of the sample which used Y_2O_3 as the fluxing agent was best of all. And when the amount of Y_2O_3 is 6wt%, the flexure strength and the fracture toughness is as high as 390.28MPa and 4.4MPa�m~(1/2). It can be found that the amount of columnar crystal grains increased and slenderness ratio enlarged. It is feasible that the additive Y_2O_3 can be taken the place partly by light-rare-earth oxide and when the Y_2O_3 was substituted by Nd_2O_3 partly, the mechanical property of C3 is better than the others: the flexure strength is 483MPa and the fracture toughness is 4.9MPa�m~(1/2). Because of the additional compound rare-earth oxide additives, more long columnarβ-Sialon grains were formed in the sintering body. The toughness of the material was improved as a result of the grains full development and mutual zigzag. Liquid phase was filled into the interstice between the grains, which makes the density of the materials improve. Otherwise, the form ability of lightweight compound rare-earth for Sialon is different. With the increment of rare-earth atomic, the radius of rare-earth ionic decreases and the solid solubility of Sialon become augment, at the same time the amounts of rare-earth ions in the solid solubility of Sialon become larger.