To improve the performance of fine polarization maintaining fiber (PMF) couplers, it is necessary to increase the detection accuracy of polarization axis. The mathematical model of panda PMF index is established, and then the side view method is simulated. From the simulation results, the light is transmitted in the optical fiber and is focused on the other side, and the maximum light intensity of the fiber image is related to the rotation angle and the observation distance. When the observation distance is constant, the maximum value of light intensity changes periodically with the PMF rotation angle. When the observation plane is near the focused one of the transmitted light, the highest light intensity of optical image reaches the maximum value, which is the polarization axis detection parameter of PMF. Based on this, detection method which takes the maximum intensity as the feature is proposed. Combining the micro-vision technology, the polarization axis detection system for fine PMF is designed. The image sharpness function which can confirm the position of the detection plane is proposed. The experimental data are processed using the Fourier filtering method. By fitting the experiment data with the cubic spline method, the panda PMF polarization axis is determined. According to the experimental results, the repetitive detection error is 0.61°, which meets the requirements of PMF coupler manufacturing.