The secondary lining of highway tunnels is mostly constructed on site, with low early strength and difficulty in maintenance. According to the experience of underground engineering construction at home and abroad, the use of prefabricated assembly technology can effectively solve the above problems. Through the numerical simulation of the full-section tunnel construction, this paper studies the deformation characteristics of surrounding rock and the stress characteristics of the supporting structure under the two assembly opportunities of precast secondary lining. The research results show that under the condition of continuous assembly, the surrounding rock deformation rate is faster, the final deformation value is larger, and the initial support bears most of the load; under immediate assembly conditions, the surrounding rock deformation is small, and the prefabricated secondary lining can effectively improve the initial support force. The research results can provide a theoretical reference for the prefabricated secondary lining reasonable support timing for the fabricated tunnel.