Through the field test on the laboratory building foundation pit engineering of Northeastern University at Qinhuangdao, the distribution and variation rule of steel stress and pile moment is researched and analyzed in the process of the deep foundation pit excavation. The result shows that foundation pit excavation and applied prestressed anchor are the main factors of pile internal force change, furthermore, the latter is more effective than the former. Meanwhile, the influence of top beam to steel stress and moment of pile head can not be ignored especially. The zero position of steel stress and pile moment are basically same, which lies under foundation pit bottom. The use of limit equilibrium method more economical than elastic subgrade method in design over foundation pit bottom, however, which is opposite under it.