By analyzing and studying the historical fire cases of urban tunnels, the potential problems in the fire alarm system are summarized. The optimization and solving schemes are specially proposed. The problems are studied and solved through the intelligent means. The man-machine monitoring graphical interface of the system is optimized. The emergency backup functions are added. The second alignment between each rain valve group and monitoring camera is carried out to improve the fault tolerance rate and alignment accuracy of the system. The effects are tested through the test cases. When the on-site fire alarm (fiber grating, dual-wavelength flame detector) fails to detect the fire signal due to the environmental reasons, but the video event detection or manual work through the large screen video to judge the fire situation, the on-site rain valve group can be reserved and accurately opened. And the relevant pre-arranged planning can be started through the digital twin technology.