The critical temperature( T c)is a key parameter for prediction of thermodynamic and transport properties by the principle of corresponding states.However

reliable experimental measurements of T c are restricted to stable substances.As a result

numerous estimation methods have become popular for calculation of T c.Among various methods for extimating T c

the group-contribution approach has been widely used.However most methods meed T b of the compounds

and it is difficult to measure T b of unstable substances. In this paper

an estimating method using the d 20 4 for critical properties in group-contribution method was presented and assessed.For correcting the influence of adjacent group and differentiating isomers

the new methods including first-level group-contribution method and second-level group-contribution method are proposed.70 first level groups and 34 second level groups were divided

and the contribution parameters of the groups for T c were obtained by correlating the experimental critical temperature of 325 substances

which are divided into 12 types. The average correlation error of GR1 method and GR2 method for T c is 2.950% and 1.937%

respectively.If the experimental T b is not available

the new method can be used to give satisfactory estimation. The T c of 31 compounds were predicted using the new method and Constantinou-Gani method

respectively

and the results show that the new method demonstrates singnificant improvements in accuracy.