Abstract: In this paper, the method to calculate the radioactive source terms released to the environment is provided based on the analysis results of samples in the containment atmosphere during an accident at a PWR Nuclear Power Plant, relevant factors are discussed, and the validity is verified through the comparison of results calculated by this method and the code RASCAL4.2, which is a radiological assessment system for consequence analysis. Meanwhile, some deficiencies of the code RASCAL4.2 are founded during the verification, and improvement suggestions are provided for the code.