Abstract: To evaluate the welding failure mechanism of waterproof boards in tunnel construction, optimize the welding process parameters of waterproof boards, and study the welding failure of waterproof boards in tunnel construction under different cooling rates. Establish a model of high-density polyethylene (HDPE) waterproof board using finite element analysis method and simulate the welding process. Compare the failure behavior of welded joints under four cooling rates: 27.0 ℃/min, 21.6 ℃/min, 18.6 ℃/min, and 17.4 ℃/min. Through simulation analysis, it was found that among the four groups of waterproof board welding specimens, the peak stress of the waterproof board was the lowest and the residual stress distribution was more uniform when the cooling rate was 18.6 ℃/min; At the same cooling rate, the tensile and bending properties of the welded joint are relatively excellent, ensuring good deformation ability; In the fatigue simulation experiment, the waterproof board specimen with a cooling rate of 18.6 ℃/min had the longest fatigue life, the least degree of damage concentration, and the highest peel strength during the peeling process. Therefore, 18.6 ℃/min is the optimal cooling rate for welding HDPE waterproof boards, which can effectively reduce the risk of failure of welded joints under multiple working conditions.