The invention provides a piano hinge structure, and relates to the technical field of hinges. A first fixing plate is fixedly arranged on a first hinge plate, a pin hole is formed in the first fixingplate, a first rotary shaft is fixedly arranged on a second hinge plate, a second rotary shaft is screwed to an end bearing of the first rotary shaft, and the second rotary shaft is movably inserted into the pin hole. A first notch is formed in the second rotary shaft, a first sliding groove is formed in the first fixing plate, the first sliding groove and the pin hole are through to form a through groove, the second rotary shaft is slidingly arranged in the through groove through the first notch, a second fixing plate is fixedly arranged on the second rotary shaft, a torsional spring sleevesthe first rotary shaft, one pedestal of the torsional spring is fixedly arranged on the second fixing plate, and the other pedestal of the torsional spring is fixedly arranged on the second hinge plate. The rotary shafts can move forwards when a cover plate is rotationally opened, the cover plate can incline to abut against side plates, and it can be guaranteed that the cover plate is stably put after being opened.