Methods are described for improving reproducibility of mass spectrum and quantitative analysis method using the same. More particularly, methods for improving reproducibility of a mass spectrum of a chemical compound, wherein temperatures of an ion generation reaction are controlled to be the same with each other, or wherein spectra of which temperature of ion generation reaction are the same with each other are selected from mass spectra of a chemical compound are described. In addition, methods for measuring an equilibrium constant of a proton transfer reaction between a matrix and an analyte at a certain temperature, for obtaining a calibration curve for quantitative analysis, and for quantitative analysis of an analyte by using mass spectra area described.