Abstract: On account of the problems that some application units can not grasp measurement conditions accurately in the process of determination of vitrinite reflectance and can not understand various factors influencing the accuracy of the measurements deeply, the paper has put forward that the measurements of vitrinite reflectance must meet the consistency principle of the instrument status and components positioning. According to this principle, the method and requirement of instrumental correction, specimen determination, result test have been established. The influences such as instrument linearity, stability, work curve, homogeneous light, temperature correction, the video window, oil immersion objective and immersion oil, focusing, specimen polishing quality on the measured value and the acts to control the error have been analyzed. On such basis, the improvement suggestions of grading measurements accuracy and the reducible instrument condition and determination process of utilizing virrinite reflectance measurements to direct production have been proposed:using 50 times dry objectives, rather than 546 nm filters and using the coating glasses with fixed reflectance value to replace gem standard slices and establishing work curve database, etc.