It is often advantageous to acquire ground-penetrating radar (GPR) measurements from antennas that are elevated above the ground surface, for example, in the detection of buried landmines. In this case, the electromagnetic (EM) wave always propagates through ground surface between the GPR and targets. Therefore, the variations of ground surface elevation will affect the propagation ray of EM wave. Accordingly, the subsurface target imaging will be deformed, especially the imaging in the horizontal slice, by the variations in elevation. In this study, we propose a fast method of topographic correction, which is based on the velocity model estimated by the elevated common midpoint GPR itself, to compensate the effects of variations in elevation. The method substitutes the air layer between the antenna and the ground with the soil layer by shifting the propagation time. The method was tested using experiment data acquired over a sloping ground surface under which a landmine model was shallowly buried. The result showed that the quality of target imaging was improved in slices, especially in the horizontal slice.