Abstract: A great exploration breakthrough has been made in the bedrock, the lower part of Oligocene(E₃¹) and the Paleocene and Eocene(E₁₊₂) hanging walls of Kunbei fault-terrace belt, where an integrated oilfield with over billion tons of oils has been discovered. With the coexistence and complex distribution of bitumen and crude oils, degrees of crude oil enrichment in this area are different in different well fields, and the exploration effect of the Well Qie-4 area in the middle was relatively poor. The biomarker correlation of source rocks, crude oils and bitumen shows that oils and bitumen in Kunbei have different origins. The crude oil was derived from the upper part of Oligocene(E₃²) mature-stage source rock in Zhahaquan sag, while the bitumen originated from the E₃¹ source rock and it has been destroyed and densified during the low evolutionary stage. Based on analyses of crude oil properties, microscopic fluorescence of reservoirs and reservoir inclusions, and combined with evolutionary features of source rocks and their structures, we confirmed that there are two stages of reservoir-forming in Kunbei area, which are the early Miocene(N₁) and the reservoir-forming stage after the late Pliocene(N₂), respectively. The current oil in the reservoirs mainly came from the second stage. The oil from the first stage mainly migrated laterally along unconformities between bed rocks and overlying sedimentary layers to form reservoirs. Because the paleo-tectonic location of the Qie-6 and Qie-12 well fields was higher than the Qie-4 well field, the scope of reservoir formation in the former was larger while compared with the latter, and its dimension of bitumen formed by later destruction was also huger. The oil from the second stage migrated firstly along the Kunbei faults to hanging walls, then laterally along unconformities and finally along main secondary faults to accumulate in the present traps. Consequently, the main secondary fault is a key factor to control the crude oil migration and accumulation. And the poor exploration effect of the Well Qie-4 area was primarily attributed to its location far away from the east fault of the Qie-16 well and disconnection of the E₁₊₂ reservoir with the Qie-163 well field.