The interface transition zone is the weakest area in mechanical properties of concrete structures, and its strength directly affects the mechanical properties of concrete. The strength and uniformity of aggregates are also the parameters that need to be focused for concrete structure design. Based on the discrete element method, the effect of aggregate strength, interfacial transition zone strength, aggregate homogeneity and size on concrete strength and deformation were studied. The results show that the crushing of aggregate provides a new path for propagation and merging of microcracks in sample, and the formation of a large number of network crack surfaces accelerates the destruction of sample. The peak strength and elastic modulus of sample increase linearly with the increase of interface transition zone strength, and the increase of interface transition zone strength reduces the radial deformation of sample. The post peak stage of stress-strain curve of concrete changes gradually from toughness to brittleness with the increase of interface transition zone strength. The aggregate strength has little effect on the peak strength and elastic modulus. The radial deformation of sample with good homogeneity of aggregate is smaller than that of sample with poor homogeneity. The peak strength and elastic modulus of sample increase with the increase of aggregate size, but the increase is far less than the increase of peak strength brought by interface strength.