Abstract: Through thermal simulation experiments on organics of different types, the authors found that there were much difference in vitrinite reflectance for different organics subjected to same thermal evolution. The difference for R°could reach as much as 0.24-0.60 with same thermal gradient. At low thermal stage (360℃), the values of R° for type I were lower than those for type Ⅲ;and at high thermal stage, with contrary results come about. This phenomena tallies with the observations from field sections, suggesting that vitrinite reflectance is influenced by the type of parent material. In view of above-mentioned facts,vitrinite reflectance as a general "criterion" for maturity can be applicable only for the same kind of organics, but it is difficult to use it in comparisions of different types of organics, therefore it can not be taken as a general "criterion", and correction need to be made.