Post peak deformation characteristics of plastic concrete were studied using uniaxial and true triaxial compression tests. The results show that post peak deformation characteristics are greatly influenced by confining conditions. Post peak deformation of plastic concrete becomes softened under uniaxial stress state. It will be ideally plastic or approximately plastic under true triaxial stress state with constant confining pressure, and hardened under true triaxial compression state with constant lateral displacement. The parameter of D2 can distinguish post peak deformation characteristics of plastic concrete. Post peak deformation will be hardened when D2 is positive, and ideally plastic or approximately plastic when D2 is from -01 to 0，and softened when D2 is less than -01.