Based on the steady—-state catalytic theory system，genetic types of crude oils in the Tarim and relative composition of the C7 hydrocarbon basin have systematically been studied．Accord— ing to the genetic types，the paper suggests that crude oils in the Tarim basin fall into four kinds： marine oil，lacustrine oil，mixed oil and coal—related oil，of which marine oil represents the major— ity of found in the area and is mainly distributed in Lunnan，Donghejang，Tazhong and other oil— fields．Continental oils and coal—related oils mainly occur in the Luntai fault uplift and Kuche de- pression．The values of Imcc6 vary greatly in different genetic types of oils，from less 35％±2 for marine oils to more than 65％士2 for coal—related oils．These Imcc6 values show a process of progressive variation from marine oils to coal—related oils．