Abstract: The soft coal is difficult to process into standard coal sample, so the acquisition of soft coal mechanical parameter is very difficult. By introducing granular material mechanics to the coal field, soft coal cohesion c and internal friction angle φ are obtained by combining the granular material mechanics test with Hoek-Brown strength criterion. Uniaxial compressive strength of soft coal is got according to Mohr-Coulomb strength criterion. On this basis, other mechanical parameters of soft coal can be estimated by combining the generalized Mohr-Coulomb strength criterion with geological strength index GSI.