The invention provides a coaxiality measuring method for a pin hole of a fork ear and lug assembly. The method comprises the steps that S1) a camera and a light source are mounted at the two sides of a pinhole of a fork ear along the axis of the pinhole respectively, so that light emitted by the light source can be captured by the camera by passing through the pinhole of the fork ear; S2) a lug is mounted in the fork ear to form the fork ear and lug assembly, so that a pinhole of the lug is partially overlapped with the pinhole of the fork ear, and light can be transmitted; S3) the light source is opened, and the camera is used to shoot a pinhole image of the fork ear and lug assembly along the axial direction of the pinhole; S4) the image is processed, and required features are extracted from the image; and S5) whether the pinhole of the fork ear is coaxial with the pinhole of the lug is determined according to the extracted features, and if not, the deviation direction of the axis of the pinhole of the lug relative to the axis of the pinhole of the fork ear is provided. The camera is used to shoot the pinhole image of the fork ear and lug assembly along the axial direction of the pinhole, the coaxility of the pinhole of the fork ear and the pinhole of the lug is measured in real time and back fed and controlled, and the assembling precision is thus improved.