Disclosed is an underground cavity peeping device and method based on three-dimensional scanning and 3D printing. By using the underground cavity peeping device, the technical problem that conventional peeping devices cannot acquire cavity information in an omnibearing manner. The underground cavity peeping device comprises a three-dimensional probe and a connecting rod, and further comprises a 3D data collector, 3D printing equipment and a supporting frame, the three-dimensional probe is arranged on a first rotating structure which is fixed at one end of the connecting rod, the other end of the connecting rod is fixedly connected with the supporting frame through a second rotating structure, the three-dimensional probe is electrically connected with the 3D data collector through a data line, and the 3D data collector is electrically connected with the 3D printing equipment. The underground cavity peeping device is simple in structure, convenient for disassembly and assembly and convenient to operate, can detect position and surrounding rock breakage condition of an underground cavity in an omnibearing manner, can quickly re-demonstrate distribution range and spatial form characteristic of an actual cavity through 3D printing and has important practical value in reasonably determining underground cavity treatment methods of underground engineering of at present stage.