Abstract: In order to optimize the welding process of thick steel plate in steel structure building and improve the construction quality and reliability of steel structure building, the influence on the mechanical properties of 25mm thick steel plate welding joints is studied under the premise of changing the process parameters of pulse tungsten pole argon arc welding. With the 05CuPCrNi weather-resistant steel plate test with a thickness of 25mm, the influence of the steel plate on the pulse frequency, welding current, welding speed and duty ratio. The test results show that when the pulse frequency is 1Hz, the welding current is 200A, the welding speed is 450mm / min, and the duty ratio is 50%, the mechanical indexes such as tensile strength and elongation of the welding joint reach the optimal, and the application effect is better.