The management of the present building's firesafety is evaluated with one factor as the total building's loses of conflagation.It neglects the environmental factor.the mankind's productive activities,the factor of fire fighting management and the factor of remedial measure so that an evaluation of firesafety is made with different principles.In this paper,physical parameters show the idfferences in evaluation.Then a non-dimensional equivalent expression as objective function is obtained with the aid of dimensional method,which provides scientific bases for the evaluation of firesafety.