A bearing rotation angle measuring tool comprises a main undercarriage connecting support arm mounting assembly which is assembled by a bearing race and a spherical ring. The structure of the bearing rotation angle measuring tool is characterized in that a shaft passes through a central through hole of the spherical ring, the shaft is connected with a disc-shaped spacer I, the other side of the shaft is sequentially sleeved with a spacer II and a nut at a joint of the spacer I and the side surface of the spherical ring, the spacer II can move on the shaft, the spacer II is in contact with the other side surface of the spherical ring and tightly clamped between the spherical ring and the nut by screwing the nut down, and the end part on one side, provided with the nut, of the shaft is further hung with a weight through a hanging ring. Through the structure and method, the bearing rotation angle measuring tool increases assembly quality, provides a basis for similar bearings, ensures the quality of parts, improves the assembly efficiency, standardizes the installation, and solves the technical problems in the prior art that the measuring error is large, the measuring state is unstable and the complete controllability of product quality cannot be ensured since a mandrel and a spring balance are used for measuring rotation angle of the spherical ring manually.