Abstract: The oblique angle of the fiber coupling to the upper surface of the optical chip, is one of the key factors affecting the optical coupling efficiency. Contrary to the low efficiency, poor precision and instability of the traditional angle measurement methods, the coordinate system re-establishment method combined the image processing technology were adopted to realize the rapid and precise measurement of the oblique angles. Firstly, based on conventional image angle measurement method, a targeted checkerboard was introduced to calibrate coordinate system, thus reducing the errors caused by slight rotations of the optical axis, which would happen at the time that the CCD optical amplification system acquiring the image information of the tiny optical fiber. Then to reduce the influence of noise while ensuring the detection accuracy of the linear characteristics of the fiber, Hough transform method and image thinning method, which were two classic methods to extract the linear parameters of the fiber, were compared. Combining the triangular relationship of the linear elements on the projection surface, the oblique angle of the coupling fiber was finally obtained. The experimental results show that the line extraction algorithm based on Hough transform can measure oblique angle of the coupling fiber optic under small size with higher accuracy and speed, the error is about 0.1 and the average operation time is 0.370 seconds.