The foreland thrustfold belt in south Dabashan is located between Chengkou fracture and TiexiWuxi buried fracture. To study the influence of tectonic activity on the hydrocarbon migration and preservation of shale gas, this study carried out analysis of C and O isotope for fluid inclusions from the Dabashan foreland structural belt. The results show that the distribution of the fluid carbon and oxygen isotope is more dispersed than that of surrounding rocks. And the δ13C PDB is distributed between 2.9‰ and 3.9‰, which belongs to normal marine carbonate carbon layer. The liquid near the Pingba fault shows depleted in δ13 CPDB, showing characteristic of foreign fluid mixing. The fluid inclusions consist of hydrocarbonbearing gas and liquid two phases, with gas phase of CH4 and liquid phase of H2O. Homogenization temperature of vaporliquid aqueous inclusions is the highest in that of fluids near the Chengkou fault, and range from 311℃ to 336℃ with a peak of 328℃. Southwardly, homogenization temperature is from 183℃ to 269℃ in the imbricated thrust zone with a peak of 230℃, has a peak of 213℃ in the thrustfold belt and 170℃ in decollement fold belt, displaying a gradually decreasing trend toward the basin. Salinities of vaporliquid aqueous inclusions are from 4.43% to 8.6% NaCl. The study shows that the Chengkou fracture, as a major fault dividing the north and the south boundary of the Dabashan tectonic belt, has high temperature and thermal evolution degree of the ancient fluid. The thermal evolution degree, rockforming temperature and the ancient fluid pressure increase gradually from the basin northwards the Chengkou fracture, suggesting that with strengthening of the tectonic activity, fluids in the structural belt are more active and lasts longer, resulting in that depth and temperature of fluid vary greatly. The liquid in the structural belt was overall formed in a closed system. The deep hydrocarbon fluid driven by the main tectonic stress migrated along fractures up to the shallow part of the basin, and then mixed with the shallow formation fluid. However, some secondary fractures have the limited impact on fluid sealing because their forming time and insufficient depth can not reach the lower Paleozoic hydrocarbon source rock.