The Triassic Yanchang Formation and the Jurassic Yan'an Formation are the main oil-bearing strata in Ordos Basin. Based on the study of petroleum geological conditions in Ordos Basin, sedimentary facies, oil immigration pathway, abnormal pressure, and tectonics are proposed as controlling factors of Mesozoic oil reservoir. The patterns of the Triassic oil accumulation in large-scale deltas and the Jurassic oil accumulation controlled by paleo-geomorphology are setup. Combining with the oil exploration results of the basin, the quantity and the spatial distribution of oil resource are predicted with the "layer zone" as the basic unit of resource evaluation. The results show that the amount of oil resource is 146.50×108 t, including 116.50×108 t of conventional oil and 30.00×108 t of tight oil. With respect to strata, the amounts of oil resources of the Triassic and the Jurassic are 137.20×108 t(including 30.00×108 t of tight oil) and 9.30×108 t respectively. The amount of the remaining oil resource is 96.93×108 t, most of which are distributed in Jiyuan, Longdong, and Zhijing-Ansai areas. Chang 6 and Chang 8 of the Yanchang Formation and the Jurassic are key strata for oil exploration in the future; Chang 9 and Chang 10 in the lower part of the Yanchang Formation are new target strata; the tight oil of Chang 7 has great potential for next exploration.