Abstract: With five or nine points combination, a log curve of digital sonic integral transit time is handled by the method of successive discrimination and interpolation of distortion POints. According to the high-lower limites of sonic speed of local area stratas, whether or not suddenly changes of the current and nearby points are distinguished in the combination, and the unnormal points of interval transit time are deleted. After rejecting the distortion point, the current distortion interval transit time point is interpolated by the varying rate of maximal interval transit time of interface and the curve form and the distribution type of unnormal point.