Abstract: The thermal shroud is an important subsystem of the space environment simulator, mainly used to provide a cold and dark environmental for the spacecraft thermal balance and thermal vacuum tests. The thermal shroud of the KM8 space environment simulator used for the space station thermal test and the KM7A space environment simulator used for the satellite test are all in stainless steel plate-style structures. For the manufacture of the two large stainless steel thermal shrouds, the urgent need is to solve the bottleneck problem related with the processing of the stainless steel plate-style thermal shrouds. This paper analyzes the laser welding process for the KM8 thermal shroud. Welding specimens of different combinations of plate thickness with different welding parameters are made, and mechanical tensile tests, weld analysis and detections are carried out. The optimum welding parameters of the combination of different thickness plates are then determined. The manufacture practice shows that the welding parameters obtained in this study are adequate.