The method determines the incidence angle for every ray through scanning,and hence has very large computation work and needs to provide a relative precise preliminary geologic model.This paper introduces a kind of travel time inversion method based on polynomial.First,the depth and slowness can be expressed by Chebyshev polynomial.Then the structure and velocity variation of the complex construction can be acquired through iteration.Compared with the grid velocity inversion,this method has less unknown numbers,and does not need to provide a precise preliminary geological model.Model calculations show that the result achieved is close to the actual geologic model.