Based on the calculation and simulation technology of welding temperature field, the numerical simulation of welding temperature field of thick plate joint under low temperature environment was carried out. Taking the 90 mm Q460GJC +30mm Q355C joint of high-strength building structural steel plate as the research object, the welding test and numerical simulation were carried out under a -15 °C environment, and the evolution process of multi-layer welding temperature field under ultra-thick plate was analyzed, and the performance of welding joints of large steel structure was predicted from the microscopic level. At the same time, this study provides technical support for the application of low-temperature welding, which is of great significance to ensure the welding quality of steel structures under low-temperature environment.