Nuclear magnetic resonance(NMR)and nuclear magnetic resonance cryoporometry(NMRC)experiments are carried out to quantitatively characterize the pore structure of shale gas reservoirs of Longmaxi Formation in southeast Sichuan Basin.The results show that:(1)Four types of pore are developed in the shale of the study area:organic matter pores,intra-granular pores,intergranular pores and micro-fractures.The pore size distribution of the shale is widely distributed,and the pore size is mainly between 1 and 100 nm.The reservoir space is dominated by mesopores,accounting for 76.2，,followed by macropores,accounting for 21.9，,and micropores contribute the least,accounting for only 2.0，.(2)The pore size distribution characteristics revealed by NMRC are more accurate,especially for the pore characterization in the range of 2-100 nm,which is more advantageous for the pore characterization of shale reservoirs with strong heterogeneity.(3)NMR characterization of reservoir pore size distribution is affected by many factors.The development of shale lamellation and the properties of saturated fluid will affect the NMR experiment,and then affect the characterization results of pore size distribution.The characterization of pore size distribution by NMRC method is affected by the KGT value of probe liquid and the size of the sample.It is necessary to calibrate the KGT value of probe liquid reasonably and select a suitable sample size to obtain reliable characterization results.The research results have reference and guiding significance for pore structure characterization of shale reservoir.