The Zhongwei area of Helan Mountains is a new prospecting area that was registered by the Shengli Oilfield Company of SINOPEC in August 2002. So far, no drilling data concerning the Zhongwei prospecting area has been obtained and the exploration degree is quite low as a whole. To study the hydrocarbon-generating capability of the Upper Triassic source rocks in Zhongwei prospecting area, the Upper Triassic dark mudstones in Rujigou area in the north of Zhongwei prospecting area have been collected and analyzed. The results indicates: 1) The content of organic carbon is 3.03%, and the total HC content is 0.0025% ; 2) The kerogen maceral are mainly vitrinite, and the type of organic matter in the mudstones is type-Ⅲ kerogen whose index is -72.5. The vitrinite reflectivity of the samples is 0.93%, and the thermal evolution of the organic material has reached maturity degree. Compared with the Yanchang Formation and the Carboniferous - Permian coal measures in the Ordos Basin, the organic matter of the Upper Triassic dark mudstone samples in Rujigou area has a higher abundance and has reached a high maturity, which can become better gas source rocks. The Zhongwei prospecting area and Rujigou area was dominated by the shore-shallow lacustriine facies during the Late Triassic, and Zhongwei prospecting area is closer to the lake center, and thus the sedimentary facies is more favorable. The Upper Triassic source rocks in Zhongwei prospecting area have higher gas generating ability, and the gas exploration in this area should be strengthened on the basis of the source rock evaluation.