Urban railway is a typical complex and high safety risk project. Scholars try to improve construction safety risk management level by using the theory of knowledge integration, to avoid the construction accidents. Because of the lack of systematic analysis of the construction safety risk management and the influence of knowledge integration, the purpose and direction of knowledge integration is not explicit. In order to realize the development of knowledge integration in the field of construction safety risk management, Using system theory, control theory and information theory to analyze the structure and function of urban railway construction safety risk management system, then taking the information constraint as breakthrough point, analysising the influence of knowledge integration on system function. The results show that：influence of the system function is reflected in three aspects, including cognitive objective, timely decision and reasonable management and control.