A solving spherical target imaging coordinate method based on monocular vision for resolving the deviation between the two-dimensional elliptical image center and the actual spherical center imaging coordinate in the monocular vision measurement system of the spherical auxiliary target is proposed as a result of this non-collinearity of the optical axis and the spherical center. First, the monocular imaging system is calibrated, the factors influencing the deviation between the spherical center imaging coordinate and the corresponding two-dimensional elliptical image center are examined, and the monocular spherical center imaging coordinate solution model is developed. Second, the improved Zernike moment method is used to realize the edge sub-pixel extraction of ellipse images. The simulation results demonstrate that the ellipse center positioning accuracy of the improved Zernike moment method is enhanced by more than 25.00%. Finally, the experimental plan for the monocular measurement of the spherical target distance is created, and the experimental validation is done on spherical targets with various intervals. The findings indicate that the maximum absolute deviation between the spherical target moving distance calculated by the proposed method and the actual value is less than 0.039 mm, which meets the requirements of target positioning accuracy and stability of monocular vision robot system.