Abstract: After briefly reviewing the development process of vitrinite reflectance (VR), summarizing the main application aspects of VR in the field of petroleum geology, the paper focused on discussing the factors influencing the results of the VR measurement. All of the factors either belong to geological or belong to man-involved ones, they can be divided into four major aspects:the limitations of the VR itself, the kerogen type and the lithological difference of hydrocarbon source rock, the processes of collecting and dealing with the samples and the process of determining the VR. The results of the VR measurement just are the reflection of interaction of these factors. According to overstated discussion,several advices are proposed for the relevant researcher at last.