Abstract:This paper introduce non-probabilistic interval assessment method to evaluate the crack of the steel beam’s safety. This approach consists of three elements: an interval defect assessment curve, evaluation defined rectangular diagram for non-probabilistic reliability, based on the theory of interval, such as crack size, material properties, loads are defined as uncertain parameters. Finally, through numerical simulation with fracture of the steel uncertain interval parameters, the non-probabilistic reliability evaluation method of crack in the safety assessment, then evaluation results and the method of reliability are compared and analyzed, which verify the accuracy of the method.