The Yanchang Formation of the Triassic in the Ordos Basin mainly developed two sedimentary systems: northeastern and southwestern systems. It has been proved that the northeastern sedimentary system belongs to the river delta system through abundant research data. However, the southwestern system is studied little due to the limitation of the exploration. Through the latest drilling and outcrop data, it has been established that the southwestern sedimentary system in the Ordos Basin belongs to the alluvial fan—fan delta system and the alluvial fan, fan delta and lake facies or turbidite facies were developed. The alluvial fan is representative in the sections of Pingliang Kongdongshan and Ruishuihe River. The fan delta and lake facies or turbidite facies are proved by the drilling sections in the study area. The main reservoirs include intervals Chang6 to Chang8 and the strata is preserved integratedly with the relatively high drilling degree. The subaqueous distributary channel is the main type of the fan delta front while the channel mouth bar is developed locally. The turbidite sandstone is mainly thick- bedded. Fan delta front subfacies was most developed during the Chang8 subage. Three delta front sand belts are formed from southwest to northeast and they are the important areas where hydrocarbon accumulates. The turbidite system was considerably developed in the Chang7 Subage because the lake basin subsided, the periphery was uplifted strongly and the lakeshore was very steep. The fan delta was developed again because the lake regressived during the Chang6 Subage, but the scale was smaller than that of the Chang8 Subage. The fan delta front sand body is the most advantageous zone of petroleum accumulation because its great thickness, coarse grain, well sorting and good physical properties.