A data processing method for creating simulation data of a three-dimensional chromatogram for a sample containing a plurality of components. The data processing method includes a data preparing step of preparing chromatogram data and spectrum data of each of a plurality of the components, a parameter determining step of determining a parameter including a ratio of concentration of a plurality of the components in the sample to each other and separation degree of peaks of a plurality of the components on a chromatogram from each other, a data adjusting step of adjusting a peak area and a peak position of chromatogram data of each of a plurality of the components based on the parameter determined in the parameter determining step, and a matrix product step of calculating matrix product of a spectrum data group including spectrum data of each of a plurality of the components and a chromatogram data group including chromatogram data of each of a plurality of the components adjusted in the data adjusting step, and creating simulation data of a three-dimensional chromatogram for the sample based on a result of the calculation.