A new method is proposed to estimate the heat or vaporization of pure liquid at its normal boiling temperature. The properties required include the boiling temperature, critical temperature and critical pressure. For monohydric alcohol and monohydric organic acid, an adjusting-boiling-temperature strategy is proposed to reduce the calculation errors. The method is tested for 160 substances including many groups of compounds. The results show that the proposed method is better than the literature methods, especially for monohydric alcohol and monohydric acid.