21 bituminous sandstone samples of Chang-8 member in southwestern Orders Basin were collected, and the biomarkers of bitumen were detected by means of GC-MS. The compositional and distributional characteristics of biomarker compounds of bitumen samples were studied and the origin of bitumen is discussed. The result shows that:(1) The relative content of tetracyclic terpane to hopanes and C29 regular steranes to C27 are high, C24 tetracyclic terpane/(C24 tetracyclic terpane+C26 tricyclic terpane) ranges from 0.26 to 0.52,C23 tricyclic terpane/(C23 tricyclic terpane+C30 hopanes) ranges from 0.06 to 0.41, these data indicate that their organic parent materials are mixed ones and the higher land plants make a great contribution to the oil generation. (2) The low-content ofβ-carotane, gammacerane and C30+hopanes,and that the ratio of Pr/Ph is 0.67~1.07,indicate that the oil was formed under the weak oxidizing to weak reducing freshwater or brackish-water lacustrine environment. (3) Several ratios, including C31 hopanes 22S/(22S+22R),C29 sterane 20S/(20S+20R),C29 sterane ββ(/αα+ββ) and C29 diasterane 20S/(20S+20R), completely or almost completely reached such equilibrium value that it indicates the studied bitumens are mature. The results of oil-source rock correlation show that the geochemical characteristics of bitumen in sandstone of Chang-8 Member from southwest area of Ordos Basin are similar to those of the upper Triassic Chang-7 subsection, so it is proposed that the bitumen originated mainly from the Chang-7 source rock.