Car coupler free rotation angle measuring device and car coupler free rotation angle measuring method

The invention provides a coupler free rotation angle measuring device and a coupler free rotation angle measuring method. The coupler free rotation angle measuring device comprises a base, an angle scale, a rotating rod, a sliding block, a coupler rod and a pair of calipers. The base is used for being detachably fixed to a coupler yoke. The angle scale is arranged on one side of the base along the first direction and is fan-shaped; the rotating rod is provided with a connecting end and a free end, the connecting end is rotationally connected to the base, the rotating axis of the connecting end and the base coincides with the sector circle center, corresponding to the angle scale, of the base, the position, close to the connecting end, of the rotating rod is provided with a tip, the sharp end of the tip is located on the periphery of the angle scale, and the rotating rod is further provided with a guide groove and first length scales; a sliding block is arranged in the guide groove in a sliding manner; one end