Since the 4f optic information system composed of general equipments has not enough space invariant character, an improved method is presented to achieve inverse filtering denoising under the general condition. The step function response is obtained by taking advantage of the parallel processing of the 4f system and the linear theory is used to realize the inverse filtering denoising of the output image. Experiments show that the method can achieve the inverse filtering denoising, remarkably improve quality of the optic image and keep the detailed information under the current condition. Furthermore, the method doses not increase the complexity and time of the optic experiment. At the same time, it decreases the complexity and time of calculation of inversing filtering.