Abstract: In order to get the physical objective of the long pulse operation in HT 7U device, in the research of the doped graphite and in the control for most impurities and recycling in the steady state of the long flat period, a concept of developing functionally gradient coatings with the good sputtering resistance was presented . The methods of thick SiC gradient coatings by CVR and CVI are studied, SiC coatings by CVI are found thicker, morecompact， better gradient and good thermal shock resistance,which is adaptable to protective coatings on the high heat flux components of HT 7U device.