Assessing residual moveout after migration is a useful way to undertake velocity analysis in surface seismic data. In this paper, we apply this concept to walk-away vertical seismic profile (VSP) data. Because of the non-symmetric source and receiver geometry, it is hard to detect the depth residual moveout in conventional common image gathers (CIGs) for VSP data. In this case, we changed the horizontal axis from horizontal offsets from the common image point (CIP) to be receiver depths. We derive a residual moveout function for migrated common receiver gathers assuming a constant velocity model having a single horizontal reflector....