All studies demonstrated that a problem-invariant parameter Mc (the critical value of the M-integral) can be possibly proposed as a possible damage parameter for describing the degradation of material and structural integrity caused by irreversible evolution of multiple defects.And the M-integral is emerged as a damage criterion to be capable of describing the damage behavior of a multi-damaged mechanical system similar as the J-integral in fracture mechanics as a fracture criterion.Furthermore,it can provide some outside variable features which might open a new technique or framework to evaluate material damage evolution.