1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. Key Laboratory for Evolution of Past Life and Environment in Northeast Asia(Jilin University), Ministry of Education, Changchun 130026, China;
3. Oil & Gas Survey, China Geological Survey, Beijing 100029, China;
4. Jilin Geological Exploration Institute, China Chemical Geology and Mine Bureau, Changchun 130022, China;
5. Oil & Gas Survey, China Geological Survey, China Chemical Geology and Mine Bureau Oil Sands Geological Survey and Technology Research and Development Laboratory, Changchun 130022, China

Continuous samples of different depths in one layer of Xiaotaipingshan were used for geochemistry and biodegradation analysis. The oil in Xiaotaipingshan oil sands reservoirs generated abundant 25-norhopanes after biodegradation. Conventional hopane and sterane also have been biodegraded. Because of the differences in molecular structure and stability, the biomarkers have different abilities to resist biodegradation. Based on C₂₁/C₂₃ tricyclic terpane, gammacerane/C₃₀ hopane, Ts/Tm, C₃₀ rearranged hopane/C₃₀ hopane, ������C₂₇R/������C₂₉R sterane, C₂₈������R/C₂₉������R sterane, C₂₉������20R/���¦�20S sterane, C₂₉������20R/���¦�20R sterane, C₂₇ diasteranes/(regular steranes+diasteranes) and the ratios of hopane isomers biodegraded to 25-norhopanes, it is indicated that the biodegradation degrees of tar sands oil increase with depths. The degradation degrees of tar sands oil also increase with water saturations, which proves that formation water is beneficial to the migration of bacterial microbes, transmission of nutrients, biodegradation of oil and generation of 25-norhopanes.