Abstract: In order to obtain the temperature field variation of the pulsed reactor in pulse operation, a transient thermal analysis sub-channel code named PRC-STAC was developed. It’s applicable to the pulsed reactor at low temperature and atmospheric pressure. Compared with the transient parameters of the TRIGA MARK Ⅱ reactor, the correctness of the PRC-STAC code was validated. The transient thermal parameters of the Xi’an Pulsed Reactor were calculated with the PRC-STAC, and the safety influence on the fuel element in pulse operation was discussed finally.