The invention discloses a geological radar detection assisting device for railway tunnels and a using method. The device comprises a lifting platform, and the top of the lifting platform is connected with a transverse or vertical frame type guide rail through connecting fasteners. A pulley is fixed at one end of the frame type guide rail, and a wire spool is fixed at the other end. The wire spool is connected with a slip rope extending into the frame type guide rail, the slip rope is connected with a geological radar, the geological radar is connected with a traction rope, the traction rope bypasses the pulley and is then connected with a traction lifting device, and the traction lifting device pulls the traction rope and further drives the geological radar to move so as to complete automatic detection. Compared with manual operation, mechanical operation makes uniform movement of a radar antenna easier to control, and therefore, detection error caused by non-uniform movement of a radar antenna which is held by an operator is avoided, and the efficiency of detection and the accuracy of prediction are improved.