Abstract: The genetic relation hip of oil and rock in Yanchang and Yanan Formations in Weibei area and the characteristics of the biotic source were correlatively analysed by means of indexec of oil and biotic sources of biotic guide compounds,It is considered that the source rack of sandy oil reservoirs in yanchang Formation and crnde oil in coal seams in the Yanan Formation is dark macstone in the second and the third members of Yanchang Formation, The physical property differences of crude oil in different strata were mainly resulted from, the secondary degrardation.