Abstract: The paper analyzes and compares the biomarkers in the products from asphaltene thermal simulation at different temperatures in normal crude oil and heavy oil suffered from serious biodegradation in the northwestern margin of Junggar basin. The results show that relatively ideal temperature for the thermal simulation is 300℃, at which biomarker composition distribution of the products from the asphaltene thermal simulation of heavy oil is in accordance with that of normal crude oil. The biomarker in the simulation products of the heavy oil has complete compositions, indicating that it didn’t suffer from biodegradation and can be used to do oil source analysis for seriously biodegraded oil, which is featured with relatively high Pr/nC17 and Ph/nC18（0.66~0.71 and 1.01~1.21, respectively), relatively low Pr/Ph （1.15~1.21) and relatively high gammacerane index (0.30~0.41), indicating a weak reducing-reducing and brackish water-saline water depositional environment of organic parent materials; a C20＞C21＞C23 distribution pattern of tricyclic terpane and C23 tricyclic terpane/(C30 hopane + C23 tricyclic terpane) of 0.46~0.49; and extremely low content of Ts and C29Ts, showing that it is almost the same to the biomarker in the typical source rocks of Fengcheng formation