A method for determining a physical similarity simulation material of a solid backfill body is provided. A compaction test is run on a gangue backfill body in a lab, to obtain a ε-σ curve regarding the gangue backfill body in the compaction process. Backfill blocks are made by using a thin wood board, sponge, and a paper sheet in different proportions, and then an unconfined compression test is separately run on the backfill blocks used for physical similarity simulation, to obtain εi-σi curves regarding the backfill blocks in the compression process. A sum of squared errors Σ(εi−ε0)2 is introduced to separately calculate a sum of squared errors of the backfill block and that of the gangue backfill body, and accordingly an error between ε-σ curves regarding the test block and the gangue backfill body is determined. Finally, a backfill block for which the sum of squared errors is less than 0.5 is determined as a physical similarity simulation material of the gangue backfill body. By fabrication and selection of similar materials, the present invention can reduce an error caused by a selected backfilling material during a physical similarity simulation experiment, guaranteeing the accuracy of the physical similarity simulation experiment for solid backfill mining.