Abstract: Isomers have similar mass spectra but different retention index in GC/MS qualitative analysis. The results can be wrong with the identification of chemical constituents based on the comparison of mass spectra alone. Linear regression method had been presented to study the retention index and retention temperature of compounds from two published papers. Some mistakes with the constituent identification in these papers were found and revised. The regression method presented can simplify the determination of retention indices of component peaks. It provides a powerful method in sample analysis.