Abstract: Due to the size limitation of the laboratory test equipment, the maximum particle size of the dam material has to be scaled down to the allowable size of the laboratory test equipment, and the particle size scaling would lead to changes in the test parameters. The results of the dry density, permeability coefficient, and triaxial shear tests for a barrier dam material with different maximum particle sizes show that the reduction in size leads to an increase in the content of fine particles less than 5 mm and affects the degree of compactness; as the maximum particle size decreases, the permeability coefficient of the specimen gradually decreases, and the direct use of the reduced size test results will overestimate the impermeability of the barrier dam material. Contraction rule has little effect on the strength index \varphi value, but as the sample of maximum particle size decreases, the Duncan-Chang model parameters K and K_b increase; as n and m decrease, the test results of the scaled size overestimate the strength of the barrier dam material and the ability of the dam to resist deformation, and the actual deformation of the dam is underestimated. The results of the study can provide an important reference for dam stability analysis and deformation analysis.