Two molding press processes with different cooling methods were adopted to manufacture poly-trifluorochloroethylene （PCTFE） seat sealing ring for ball valve. The results of cryogenic experiments show that internal micro-cracks would occur in the PCTFE product prepared by press process with natural cooling， while the one prepared by press process with pressurized cooling will not generate intrinsic micro-cracks. The results of characterizations and performance tests indicate that molding press process with natural cooling leads to occurrence of micro-cracks in the product， resulting in the subsurface defects during the cryogenic experiments and seal failure. Pressurizing the product during cooling will inhibit the occurrence of micro-cracks，avoiding the appearance of aggravated cracks due to the internal stress generated by the room-low temperature cycle condition.