Abstract: The source rocks of Aryskum depression in southern Turgay basin are mainly in Middle?Lower Jurassic, which contain three types of kerogen, i.e. humic?sapropelic, sapropelic?humic and humic ones, being at low mature?mature and locally high mature stages. Aryskum depression has a structure in alternative arrangement of sags and swells, in which oil and gas generally occur in sags with multiple sets of sources rocks and store in swells. So the oil sources is difficultly distinguished by the difference and similarity of sedimentary environment and kerogen properties between the sags and the strata. According to the data analysis, sterane in the crude oil is divided into four distribution types of Ⅱ1, Ⅱ21, Ⅱ22, III and tricyclic terpane into two series with 11 distribution types. Using "the unknown peak" of tricyclic terpane to distinguish source rocks in different sags and using distribution assembly of sterane?tricyclic terpene to find out specific position of the source rocks, by which the oil?source distinguishing problem is successfully solved