Migration velocity modeling can be implemented in various kinds of gathers. This paper puts forward the migration velocity modeling method in common focus point gathers based on the principle of equal traveltime and the differential time shift analysis. The updating of the migration velocity is realized by using model parameter constrained iterative inversion. The parameterization of the model can be determined by actual geological structure. A new parameter, i.e., the vertical velocity gradient, is selected to fit the lateral velocity variation. The test of the depressed model proves that the relative error of migration velocity is lower than 0.25%, and the absolute error of reflector depth is lower than 10 meter.