Abstract: Due to the different sources of raw materials and manufacturing processes, different automotive paint samples have different isotopic signatures, which can be used as the basis for distinguishing similar paint samples. The varnish is the paint applied on the outermost layer of the car, which is easily affected by the storage conditions. Therefore, the isotope ratios of different varnish samples under different storage conditions were analyzed. Ten automotive varnish samples were collected and stored for 6 months at room temperature away from light, high temperature of 60 ℃, low temperature of -20 ℃ and strong ultraviolet light. After that, the samples were analyzed by elemental analyzer-isotope ratio mass spectrometry (EA-IRMS). The carbon, hydrogen and oxygen isotope values were determined. The results showed that the carbon, hydrogen and oxygen isotope ratios of different paint samples can be used to distinguish different samples, the potential of identification and differentiation of paint samples using stable isotopes of carbon, hydrogen and oxygen were demonstrated. The carbon, hydrogen and oxygen isotope fractionation of the paint samples occurred under different storage conditions. The δ¹³C value of the samples shifted to a negative value after storage at high temperature and low temperature, greater variation of samples occurred at high temperature, and the influence of strong ultraviolet radiation was weak, which meant that UV light had little effect on the δ¹³C value of the paint samples. The δ²H value shifted to a positive value under the three conditions, which was most affected by ultraviolet radiation, and minimal change in the condition of high temperature. The δ¹⁸O value shifted to more negative under the three conditions. But the shift amplitude of the δ¹⁸O value was different between samples of different resin types. Among the three resin types of samples, polymethyl methacrylate lipid resin samples had the smallest offset due to the least oxygen content in the molecules, the variation ranges of glyceryl elaidate and sorbitan monostearate paint samples had little difference under the three storage conditions. Stable isotope analysis method can provide high resolution three-dimensional fingerprints for paint samples, which has great potential in paint identification applications, and can be applied to traceability analysis of paint physical evidence.