The safety risk events that may occur during the cast-in-situ process of a concrete box girder of an interchange bridge with high piers in mountainous areas are briefly listed. Based on the background of an interchange project in Yunnan province, China, the relative importance weights of selected safety risk events are calculated by an analytic hierarchy process, and the uncertainty and fuzziness of the analytic hierarchy process are solved using the cloud theory to improve the accuracy of the analytic hierarchy process; then the improved likelihood–exposure–criticality method is used to evaluate the risk level of safety risk events. It is verified that the use of back-propagation-neural network theory can realize the risk prediction of engineering projects based on human factors and environmental factors. At the same time, real-time risk prediction based on dimension and space dimension is necessary, and it also provides a new idea for security risk assessment.