Traditional inspection and focusing methods have high complexity and poor stability. This paper presents a self-collimation inspection and focusing method based on image processing. The combination of the self-collimation focusing method and image processing method can improve system applicability and inspection and focusing accuracy. An increase in system defocusing distance leads to a decrease in imaging resolution. Radial targets continuously changing in three-dimensional space are designed to avoid the problem of a small change in contrast after defocusing. In the simulation, the evaluation function operator is selected to calculate the characteristic value curves of defocusing sequence graphs of different targets. The results show that the sensitivity, unbiasedness, and unimodality of the characteristic value curves of radial targets are better than those of Lena graphs and raster targets. The self-collimation inspection and focusing method based on image processing improves the precision of the original self-collimation inspection and focusing method by approximately 19.6%, and the required amount of the tolerant defocus is satisfied.