CFG pile has many successful engineering cases in ground treatment of high buildings. Composite modulus method is recommended by “Technical Code for Ground Treatment of Buildings” JGJ 79-2002 in deformation calculation with stress ratio method formula of composite earth layer compression modulus. In this paper, a modified formula of area ratio method is put forward based on the loading test data of composite foundation. The composite foundation settlement value calculated by this method has a good agreement with the building settlement observation value.