Abstract: Aiming at the image blurring problem caused by defocusing of sensor target in the use of large-aperture optical equipment, from the image restoration method, the defocus diffusion function and defocus transfer function of optical equipment were deduced, the judgment method of image defocus degree was proposed, the mountain climbing and the inverse filtering method were used to find the best defocus value and direction and restore the blurred image into the clear image. The real-time video focusing method of large-aperture optical equipment was given and verified by experiments. The results show that this method has important promotion and application value in automatic focusing of the outfield optical equipment.