As an effective means of computational imaging, focal sweep imaging model can extend the depth of field. Based on the ambiguity function theory, we propose an inverse filtering computational imaging model based on focal sweep mode and analyze the expand performance of the depth of field. We obtain the optical transfer function of focal sweep imaging using focus error based on the relationship between the ambiguity function and the optical transfer function. A theoretical analysis of the approximate three-dimensional space invariance of the optical transfer function is given. Based on the optical transfer function, we establish an inverse filtering computational imaging model of focal sweep. Taking a concrete imaging model as an example, we analyze the influence of different scanning ranges on the expand performance of depth of field of focal sweep imaging model based on the HOPKINS criterion. Through numerical simulation, we verify the correctness of the optical transfer function of focal sweep imaging model. We analyze and compare the imaging results of focal sweep imaging model of different scanning ranges (0.09, 0.18, 0.36 mm) based on inverse filtering model. The analysis shows that the depth of field can be extended by focal sweep imaging model; the larger the sweep distance, the better the performance of the depth of field of focal sweep imaging model.