Recently, a number of experiments and theoretical researches have showed that diamond thin films，especially nanocrystalline diamond thin films, could emit electrons at very low fields, and be well suited for field emission cold cathode which is applied in many field emission applications, such as microwave vacuum devices and field emission displays.Microwave plasma chemical vapor deposition (MPCVD) ,a kind of chemical vapor deposition method with low temperature，low intensity of pressure and clearance ，is commonly used for the growth of diamond thin films.In this paper，first ,the author drew some important conclusions by analyzing several technical factors and experimental conditions which would have great influence on the quality of diamond thin films during MPCVD process，including gas proportion，the power of microwave，the plasma"s location ,the nucleation technique ,etc.. Finally，the author has successfully deposited nanocrystalline diamond thin films with 300nm crystal particles on the slick surface of silicon by using CH4/H2 gases in the MPCVD system，and the nanocrystalline diamond thin films was proved to have good field emission performance. All these researches will make the foundation for the field emission cathode of diamond films.