A method is presented, which makes it possible to calculate velocity and interface depth of the reflected wave in a vertically inhomogeneous medium. When no information from some depth range of the earth interior is received on the earth surface, the seismic wave velocity in this depth range is considered continuous and can be computed using the travel-time curve of the reflected wave of its bottom interface. Three models are studied and a good result is obtained, in which the reflected interface depth is satisfactory. As phase comparison cannot be done in most artificial seismic data, it is difficult to find the evidence for the existence of low velocity layers. The method presented here provides a solution to this problem.