The invention discloses a tunnel lining state detection device which includes a mobile work platform (40). The lower end of a mechanical bent arm (10) is connected with the work platform (40) througha rotating gear shaft (11). The mechanical bent arm (10) is curved and telescopic. The rotating gear shaft (11) is connected with a first drive mechanism which can drive the mechanical bent arm (10) to swing around the rotating gear shaft (11) as an axis. A radar antenna support trolley (30) is disposed on a slip rope (20). The radar antenna support trolley (30) can move along the slip rope (20).A geological radar antenna (31) is fixed on the radar antenna support trolley (30). The mechanical bent arm is designed on the tunnel lining state detection device, and the design idea of linear lifting of a mechanical arm is changed. The detection speed is greatly improved. The response is quick. The motion range is very small. There is basically no obstacle avoidance behavior. The detection blind area is completely eliminated. The device has stable performance.