Abstract: Based on physical properties of crude oil and related geological background,the crude oil of Leijia-Gaosheng area in western sag of Liaohe depression could be classified into extra-heavy oil,heavy oil,medium oil and light oil.At present the region mainly generate immature oil,with heavy quality and thick viscosity. With the increase of buried depth,the crude oil physical property is changing in a good trend.Horizontally,from south to north,the relative density change from light to heavy.The controlling factors of oil property are more complex.The internal cause is mainly for oil source differences,which includes parent rock types,source rock maturity and formed sedimentary environment.While the external cause is mainly by the external environment of crude oil to its secondary transformation in the process of oil and gas accumulation and late preservation,which includes oil and gas migration,fault activities,secondary changes and oilfield development.