GC and GM-MS experiments are exerted for 34 oil samples in shallow water area of Liaohe Depression. The results show that Gas chromatograms are clear, continuous and intact which means the bio-degradation can be ignored. Originally the sediments are mainly deposited under oxidization environment. The oil resource is composed by the bacteria, aquatic organisms and higher plans. The depositional environment changes from reductive type to oxidization in the W-E direction. The salt content is high. From Lingnan well area in the west to Kuihua well area in the east the oil maturity increases. According to the depositional environment, source rocks and maturity features the oil samples are divided into 3 types. A is located in the west and centre of study area and Gammacerane index is less than 0.2. B in the centre and east. A and B are different in the organic import degree. To be specific the A is mainly supported by aquatic organisms while the B by continental materials. C has high gammacerane of more than 0.55, which comes from salt water environment.