Abstract: According to the mechanism of the generation and reduction of the nuclide in the process of migration and release from the core to the containment and the environment after the pressurized water reactor (PWR) loss of coolant accident (LOCA), the calculation model of radioactive source term for LOCA was established. The comparative analysis of model calculation results was carried out. Finally, the model was applied to the source term analysis for the third generation PWR LOCA. The results show that the relative deviation between the calculation results of the model and TACTⅢ code is within ±0.05%, and the relative deviation between the iodine calculation results of the model and TITAN5 code is within ±0.5%, so the model calculation is accurate. For various nuclear motor types of PWRs, the removal mechanism and removal rate of nuclide in the containment are different, resulting in different I and Cs radioactivity release curves. The cumulative radioactivity of ¹³¹I, ¹³⁴Cs, ¹³⁶Cs and ¹³⁷Cs released into the environment within 30 d gradually increases. The established model is highly versatile, which is based on the complete nuclide decay chain, considering the contribution of the precursor nuclides decay to the daughter nuclides, and the effective removal process of elemental iodine by spraying or natural removal.