Calculation of vapor-liquid phase equilibrium was the foundation for development and design optimization of chemical processes.Focal point of the calculation was to determine relationship between four variables of temperature T

pressure p

liquid phase composition x and vapor phase composition y in any vapor-liquid phase equilibrium system.Among these four variables

it was difficult to accurately measure vapor phase composition y

especially at low vapor concentration.Therefore

y was generally calculated by thermodynamic methods after experimental determination of p

T and x.Such methods could be divided into model and model-free methods

which model-free methods got academic attractions as a result of no need to consider application limitations of various activity coefficient models.Through analysis of principles of model-free methods

recent progress with an emphasis on applicable system

convergence rate and calculation accuracy was summarized and compared from the viewpoint of direct and indirect technique.The application of several common methods was discussed and the future research of model-free methods was forecasted.