In order to understand the relationship between the parallel bond parameters in the PFC2D and the direct shear strength parameters when simulating laboratory direct shear test,a model was established based on the particle size distribution after the disintegration of mudstone in the Jianghuai test project.The influence of the parallel bond parameters in the PFC2D on the strength parameters of mudstone direct shear was studied by using the control variable method.The results show that the effects of the parallel bond parameters on the shear strength parameters are not monotonic and should be divided into different sections for discussion.The sensitivity of parallel bonding parameters to cohesion and internal friction Angle is different.