Abstract: Studies of vitrinite reflectance and illite crystallinity from Upper Sinian to Lower Triassic in Chang-yang area of Hubei Province have indicated that,there are 2 abnormal zones of equivalent vitrinite reflectance and illite crystallinity between Permian-top of Silurian and bottom of Silurian-top of Lower Cambrian.The upper abnormal zone is formed by thermal effects of advection hot liquid flowing along D₂y,S₃sh sandstone reservoir as well as D₂y/S₃sh,C₁y/D unconformity surface.The lower abnormal zone is formed by thermal convection of hot liquid in-C₁s-O reservoir.Hydrocarbon generation in P and O₃w-S₁ln should stop at the end of Middle Triassic;however,due to thermal effect of hot liquid during the Yanshanian stage,it continues to the end of Jurassic,hence favorable for petroleum accumulation.