The parameters, i.e. lining thickness and reinforced rebar of lining, and the longitudinal and circumferential length of hollow behind lining can be detected rapidly and accurately by nondestructive ground penetrating radar detection technology nowadays. However, the radial dimension of the hollow behind lining can not be clearly identified due to the difference of dielectric constant and recognition of reflecting surface. The technology of threedimensional laser scanning in borehole is adopted to detect the hollow behind lining of an operating railway tunnel in Southwest China for the first time. The threedimensional shape and sizes of the hollow are obtained based on borehole drilling method and ground penetrating radar. The detection results can provide accurate data for tunnel disease treatment and reference for pertinent and feasible tunnel disease treating schemes. The technology of geophysical prospecting+threedimensional laser scanning in borehole can detect the hollows behind tunnel lining accurately.