Abstract: The design basis source terms provide a basis for safety analysis of nuclear power plant and the foundation of the radiation shielding calculation. In this paper, based on the research of reactor core, primary loop, secondary loop and airborne radioactive source term of pressurized water reactor, migration constants and nuclear reaction constants are introduced by analogy to decay constants, then an integrated calculation method is proposed for calculating the above source terms. The aforesaid equations are solved by program based on the TTA algorithm where the discrete time approximations are applied to, taking account of the source equation characteristics of variable, coefficient, large, sparse and stiff. The results comparing with the typical pressurized water reactor engineering documents are also given in this paper, which verify the correctness and necessity of the program.