Energy transmission is an essential feature of material. Uniaxial compression test is performed by particle flow code to study crack propagation, energy transmission and damage evolution. It’s revealed to be more reasonable to research the energy through PFC, which overcomes the defect of macro mechanical theory and makes it possible to achieve multiple cracks failure form of specimen. In the compression process there is a one to one correspondence between cracks, energy and damage evolution. The relationship between macro-and micromechanical parameters is analyzed under three working conditions. It is concluded by least square fitting that microcracks are in power function with axial strain. Damage variable is defined with secant modulus. The accelerated decline of elastic modulus is taken as damage threshold which equals to 0.158. It has been proved that there is a linear regression relationship between damage and microcracks, so as to provide reference for further research on damage evolution.