Faced with the accelerated pace of shale oil exploration, it is urgent to develop a new method for shale full-pore characterization to meet the judgment of shale pore structure type. The pore structure of shale samples is dominated by micropores, mesopores and macropores, and the pore volume in each pore size range is an important factor affecting the effective value of the reservoir and the amount of oil and gas. There are various methods used to describe the pore structure characteristics of shale samples based on different theories, and even the same method has different mathematical calculation models to choose from. In this paper, after investigating and comparing the advantages and disadvantages of various measurement methods, it is determined to use the fluid method to describe the characteristics of the shale’s total pore size distribution. The micropore volume measured by CO2 and the mesopore volume measured by nitrogen gas are both characterized by the DFT model. When dealing with the intersection of mesoporous and mercury intrusion 6–40 nm data, use the integral method to calibrate the mercury intrusion with nitrogen as the standard or to calibrate the mercury intrusion with the nitrogen data as the standard to obtain the full pore size distribution map of the shale sample, after correcting the full pore size data based on the mercury intrusion data, the total pore volume measured by calculating the full pore size distribution is 23.0% smaller than the total pore volume measured by helium, with a variance of 20% and large fluctuations. The nitrogen data is used as the standard after correcting the full pore size data, the total pore volume measured by the full pore size distribution is 16% smaller than that measured by helium, with a variance of 10%, which is more stable. Therefore, a new method for describing the total pore size distribution of shale, which uses nitrogen as the standard to correct mercury intrusion, was finally established.