Abstract: According to the working conditions and technical requirements for pipe discharge muffler in passive nuclear power plant, the numerical simulation was used in analyzing sound transmission loss and fluid pressure loss of multi-section expansion muffler by finite element analysis （FEA） software ANSYS. The effect of different muffler structural parameters on sound transmission loss, passing frequency and pressure loss was also analyzed. Based on the analysis results, a reasonable combination of the muffler structural parameters was determined, and a pipe discharge muffler with good performance was obtained.