Objective To improve the calculation method for latent heat of material phase change based on T-history curve. Methods The time-temperature data measured during cooling of phase change material by the temperature logger were fitted into curves with polynomial and cubic spline interpolation, to calculate the latent heat of deionized water and hydrated salt, respectively. For phase change material without supercooling, the first derivative maximum, the point mutation in the first derivative, and the inflection of the cooling curve after fitting were used as the beginning point of phase change to calculate the latent heat, respectively. Results The deviation from the theoretical value of fitting with cubic spline interpolation was substantially less than 10% . For phase change material without supercooling, when the first derivative maximum was used as the beginning point of phase change, the maximum deviation from the theoretical value from the calculated value of latent heat was 8.01%, and the minimum was 1.55%. Conclusion Calculation of the latent heat of PCM by fitting with cubic spline interpolation was the most stable and close to the theoretical value. When the first derivative maximum was used as the beginning point of phase change to calculate the latent heat of the phase change material, the result was more accurate.