As the main absorption mode of fracturing fluid in reservoir, imbibition is an important driving force to improve shale gas productivity. In this paper, the Longmaxi formation shale in Pengshui area of Chongqing is studied. Mercury intrusion porosimetry, imbibition under different conditions and NMR tests were carried out successively. It shows that: ① The permeability and porosity of shale are very low, mainly micropores and mesopcres, almost no macropores, and the pore structure is poor; ② The process of shale imbibition can be divided into three stages. With the increase of pressure and temperature, imbibition behavior is enhanced. The imbibition effect of gel breaking fracturing fluid is slightly stronger than that of non-gel breaking fracturing fluid. Surfactant and KCl solution can reduce the imbibition ability of shale; ③ In the process of imbibition, the medium and large pores and fractures are filled with liquid in the initial stage, while the very small pores and fractures are filled first, and then the liquid enters into the slightly larger micropores and microcracks, resulting in a large number of microcracks on the surface of shale.