Abstract: Three-dimensional optical microscopic measurement technology demonstrates significant advantages in micro-hole measurement due to its non-contact nature, high precision, three-dimensional characterization capability, operational efficiency, and adaptability to complex materials. Dark field microscopic measurement technology is an effective means of measuring the three-dimensional morphology of micro-pore inner walls. A method for analyzing the imaging characteristics of micro-pore vertical inner wall with dark field microscopy was introduced, focusing on studying the core evaluation index of imaging systems - point spread function. Firstly, by analyzing the process of micro-pore dark field microscopy imaging, the corresponding relationship between the irregular pupil and the detection depth was determined, the occluded aperture point spread function was defined, and a calculation model that included geometric occlusion effects was established. Then, the influence of ratio of detection depth to diameter, imaging numerical aperture, and primary aberration on the imaging performance of micro-pore inner wall dark field microscopy was analyzed through simulation experiments, which provided theoretical guidance and technical support for the design and optimization of micro-pore inner wall dark field microscopy imaging systems. Finally, the consistency in the variation trends of the full width at half maximum (FWHM) of optical spots between simulation and experimental results further validates the theoretical model: under identical aperture obstruction conditions, the expansion trends of spot FWHM show high agreement (approximately 2-fold in simulation and 2.1-fold in experiment), effectively demonstrating the correctness of the model.