The invention discloses a detection device for a large underground horizontal dissolving cavity, and belongs to the field of underground deep special space detection and utilization. The detection device for the large underground horizontal dissolving cavity is characterized by comprising a driving propeller, a rightward rotating propeller, a driving motor, a rightward rotating motor, a battery pack, a controller, an electronic compass, a 3D sonar imager, a photovoltaic conversion interface, a towing line, a leftward rotating motor and a leftward rotating propeller. The newly-developed detection device for the large underground horizontal dissolving cavity can move by itself, and can carry out holographic measurement on the shape and the size of the abandoned horizontal rock salt dissolving cavity, the defect that an existing detection device is large in size, and cannot carry out measurement on the horizontal dissolving cavity is overcome, and real-time on-line detection can be carried out on all the water-filled underground spaces within the depth of thousands of meters.