Deep foundation pit construction has the characteristics of high risk, complex process and many disaster-causing factors. How to reasonably judge its safety state has become the primary problem to be solved in risk management and control. The analytic hierarchy process is highly integrated with the unascertained measure theory, and the risk assessment model is constructed and applied in the construction process of deep foundation pit. 22 secondary evaluation indexes were selected from four aspects of safety management, external and geological environment, construction quality and monitoring factors, and the qualitative and quantitative indexes are quantified from five levels to establish the evaluation index system. The unascertained measure theory is used to solve the single index evaluation matrix and establish the measure function. The analytic hierarchy process is used to determine the objective weight of each index, and the risk level of deep foundation pit construction is judged according to the identification criteria. The model is applied to the risk assessment of deep foundation pit construction in engineering projects. The evaluation result is level II, which belongs to low risk, which is consistent with the actual situation. The evaluation model makes a reasonable and objective evaluation of the construction risk of deep foundation pit, and provides a new method for effectively identifying and accurately evaluating the construction risk of deep project pit.