Abstract: The similarities and differences of constant mass dilution method and constant volume dilution method were researched by listing their theoretical formulas. The influence of different acidities by two methods were compared in ICP-AES, and it is found that constant mass dilution method can better adjust the negative effects of the density and viscosity of sample solutions on analysis results. Standard substances of steels were prepared by constant mass dilution method, and the multi-element calibration curves were established. The results show that the linear relationships were good. The analysis results of different matrix samples prepared by these two methods were compared, and the results were found to be consistent with each other.