In order to assess the standardization of safety accurately and objectively, this paper establishes the safety evaluation index system for the building construction according to engineering experience. The weight of each index is decided reasonably by the Analytic Hierarchy Process. Based on extension theory, the evaluation matter —element model for evaluation of construction safety is established, and the extensional evaluation method with correlative functions is put forward. Thus, construction safety is systematically evaluated. Finally it verified by project example, the result proves its feasibility.