In order to evaluate the temper effect during the multiple post weld heat treatment (PWHT) process, Thermal Cycle Tempering Parameter (TCTP) proposed by the authors, which is derived by extending Larson-Miller parameter to non-isothermal process, has been used to evaluate quantitatively the temper effect during heating and cooling processes in the process of PWHT. It has been clarified that the temper effect in the multiple PWHT process including long-time heating and cooling processes can be quantitatively evaluated by TCTP. On the basis of the present study, it might be possible to shorten the holding time of the heat treatment for multiple PWHT.