Abstract: Three types of widely used calculation methods for spray removal process and natural removal process were introduced, and the corresponding decontamination factors within 24 hours were compared in the paper. The results indicate that deviations between the methods can be significant for spray process, and calculation results for different methods have roughly same trend for natural process except the method used in RASCAL. Through this work, a more reasonable aerosol removal determination method in source term estimation is recommended to be used in nuclear emergency.