Abstract: The potential surge line break should be fully considered in the research and analysis of severe accidents for SMR. Therefore, the severe accident analysis model was established based on the design characteristics of SMR. The severe accident process is simulated, and the thermal-hydraulic phenomena and the effects of different break sizes under the pressurizer surge line break accident are analyzed. he. The results suggested that the most serious accident process happened when the break area is 0.002m². Thus, this paper suggested to use this accident as the limit condition to provide reference for the formulation of the severe accident management guideline.