Abstract: Surface free energy is meaningful as a vital characteristic of material surface energy state. As it's equal

to surface tension coefficient in value for liquid，the free energy can be got by measuring the surface tension.

Traditional methods can not guarantee both application scope and precision. As to this problem，a new method is

mentioned in this paper: Based on the Laplace's equation studying bubble films，the process of bubble gradually increasing

is considered. The data of differential pressure and related radius is dealt with by linear regression equation

to get the liquid surface tension. This method not only applies to the environment of high temperature and pressure，

but also avoids the main error source of maximum bubble pressure method without introducing new error.

Key words: surface free energy, bubble film, Laplace's equation, linear regression equation