Abstract: After a supposed accident leads high temperature gas-cooled reactor to shutdown, the heat from reactor will be removed out by the cooling system. For the 200 MW high temperature gas-cooled reactor (HTR-PM) designed by Institute of Nuclear and New Energy Technology of Tsinghua University, before the cooling water is pumped into the secondary side of steam generator, the pressure relief valve on the live-steam pipeline will open to decrease the secondary side pressure of steam generator. In this paper, a general thermal-hydraulic system analysis code was used for modeling the secondary side of the steam generator of the 200 MW high temperature gas-cooed reactor, and simulating numerically the pressure relief transient after the accident. The temperature of steam generator in the transient with different pressure relief designs was calculated and analyzed, which provides supports for the material stress analysis on steam generator and system design.