Abstract: Gas chromatography-mass spectrometry (GC-MS) analysis of the thermal simulation products of the Eocene oil shales from the Huadian Basin in Jilin province show that a series of benzohopanoids disappeared at a simulation temperature≥340℃. The benzohopane index (BHI) correlates well to the equivalent vitrinite reflectance, which can be used to judge maturity for low-maturity source rocks, and to distinguish mature and immature source rocks.