Abstract: Heat of vaporization of liquid is very important thermodynamic data for research and many applications in chemical engineering.After analyzing the drawbacks of the Watson’s equation for estimating ΔH_bi, a new equation was proposed from the viewpoint of molecular thermodynamics theory and the equation of heat of vaporization at T_b.The physical meaning of Eq.(5) was clear and definite.The average error of Eq.(5) was 0.69% for 310 experiment values.The applicable temperature range was large,from near melting point to near critical point.The accuracy of the equation was over 4.4 times higher than that of Watson’s equation for 39 structural types such as alcohol, aldehyde, ketone, ether, amine, pyrrole, pyridine, and so on, in chemical engineering, especially petrochemical engineering and fine chemicals.