Abstract: This paper analyzed the factors influence interval transit time data and introduced the method of pretreatment. According to the effective stress theorem, the physical model for stress-strain relationship of formation rock and the mechanics model for pressure calculation were set up by using interval transit time data. The calculation procedures are as follows:1. Measure sound velocity with the use of interval transit time; 2. Get effective stress by using sound velocity; 3. Calculate the overburden pressure by density logging; 4.Get formation pore pressure according to overburden pressure and effective stress. The application in Dawanqi, Yangtake area and so on in Talimu Basin showed that the method have a high prediction accuracy and can meet the engineering requirements. Compared to the conventional method, its main characteristic is that it can reduce the effect of human factors on detection results greatly without setting up trend curves. It can be applied to the pressure evaluation for successive and non-successive sedimentary formations.