Abstract: Objective In the processing of stainless steel heat sink, laser welding and pressure filling and expansion are key processes among them, the processing quality of these two processes will directly affect the formation of stainless steel heat sink and usage performance. Therefore, the welding process and pressure filling and expansion process of stainless steel heat sink are studied to ensure the reliability of heat sink processing. Methods This paper analyses the stress and deformation of stainless steel plate heat sink under different welding sequences by means of finite element simulation. Based on the initial condition of post-weld state, the stress and deformation simulation of the corresponding sequence of pressure filling and expansion process is carried out. Results The results show that the welding sequence two, that is according to the welding of the internal circular weld channel of the stainless steel plate first, and then the welding of the peripheral long straight edge weld channel, in which the internal circular weld channel is welded in the direction of the long edge of the rectangular plate sequentially, can effectively control the stress and deformation of the welding process, so that the stainless steel plate workpiece can still maintain small deformation under the condition of higher pressure charging and expanding loads. Conclusion The optimal welding sequence and pressure filling and expansion process specifications are obtained, which can provide theoretical guidance for the development and manufacture of stainless steel plate heat sinks for spacecraft.