Abstract: The Ordos basin, situated in the western part of the North China platform, has been classified as an intracrationic basin. The basin is rich in oil and gas resoureces contained three kinds of source rocks. In the exploration for oil and gas an important breakthrouths have been made in recent years. A giant gas field has been discovered in Jingbian county in the central part of the basin. Based on analyses of data of vitrinite reflectance, fluid in clusions and apatite fisson track, this paper has determined the high palaeothermal filed of the Ordos basin in the late mesozoic. The palaeotemperature in the palaeozoic strata is abort 150~240℃., the highest temperature exceeding 270℃,which is higher than the present tempreture. The palaeotemperature gradient (3. 5~-4. 0℃/100m) which is closely related to tectonic activity also exceeds that (2. 89℃/1OOm) of the present. Apatite fission track data show that there is a cooling event which ocurred in 20 to 23 Ma. The uplift scope in North shaanxi slope in the east is obviously bigger than in the Tianhuan syncline. Reseach on relations between the thermal history of the Ordos basin and oil gas fields suggests that low temperature gradients in paleozic and early mesozoic times was favourable for preservation of organic material and the gas generation stage was postponed. The late Mesozoic which is characterized by highertemperatures in the period of main gas generation and migration of paleozoic coal series and carbonates. The late gas generation stage and lack of faults were favourable for preservation of giant gas fields. The central palaeouplift in the basin which has good carbonate reservoirs and is close to gas generation regions should be first chosen as an exploration target. The southern part of the yiming uplift, the northern Part of the weibei uplift, the eastern part of the north shaanxi slope and the western part of Tianhuan syncline are also potential regions of gas migration and the reserve bases for looking for new gas fields.