Abstract: Problem of weaker diffusion control leads to decline the edge shape of retention capacity based on PDE of image denoising, and the results should be poor. For this reason, the paper proposes a diffusion control image filtering method of 45N degree rotation invariant gradient magnitude. Firstly, shortcomings of the diffusion equation are analyzed, they are gradient calculation and diffusion control. Secondly, the invariant vector gradient template is adopt through this method by introducing the rotation angle calculation of four neighborhood angle projection gradient vector in 45N degree. X and Y direction of the first order partial derivative is calculated using this template, and the consistency of gradient vector direction is counted, so the edge stopping function is adopt to obtain better diffusion control. The results of experiment show that algorithm has validity.