Abstract: Through the analysis of the optical properties of maceral images and determining microscopically the reflectance of the coal macerals, the characteristics of the semi-vitrinite group of Mesozoic coal in Xinjiang are studied. The analysis results show that there exist certain amount of semi-vitrinite group in the Mesozoic coal in the region. The content of semi-telocollinite is 49%~64% of the total amount of telocollinite and semi-telocollinite. The maximum reflectance of semi-telocollinite is 0.08%~0.13% higher than that of the telocollinite. The reflectance of semi-telocollinite is between that of the telocollinite and telinite. The reflectance of the semi-telinite is 0.28%~0.34% higher than that of telinite. From the above-mentioned results, it can be concluded that semi-telocollinite should be classified as vitrinite and it is reasonable that the semi-telinite is classified as semi-fusinite in inertinite. It is important that the semi telocollinite should not be measured as the object while determining microscopically the reflectance of vitrinite in coal. So the study is very useful for coal blending of coking coal, coal liquefaction and further coal processing and utilization.