Double-pass propagation path of residual turbulence scintillation lidar in turbulent atmosphere is studied and the expression forms of residual scintillation index acquired at the receiving terminal are obtained under the monostatic and bistatic cases, respectively. Under the condition of large aperture, the scintillation index of double-pass path is just scintillation index of spherical wave caused by the uplink path turbulence effect. By an experiment of horizontal comparison between residual turbulence scintillation lidar and scintillometer, the theoretical results are verified.