Abstract: Source term analysis which provides the fundamental data for calculation of the environmental impact of radioactive releases has a guiding significance in radiation shielding, waste disposal and nuclear facility decommission. In this work, the transformation law of radionuclides, which consists of the retention, migration, adsorption and decay, was studied in the primary and secondary coolant system of PWR. The source term calculation program DORAST which applies to the reactor systems or equipment of generation Ⅱ and generation Ⅲ was developed. The basic information of nuclides was extracted from the evaluated nuclear data library ENDF/B-Ⅶ.1. The function of DORAST is to calculate the β and γ specific activity of systems and some equipments. With the reference of AP1000 design control documents, a benchmark was designed and the calculation results were verified. The results agree well with the benchmark and it indicates that DORAST meets the computation precision of engineering design.