The　traditional　partial　differential　equation　image　denoising　model　has　the　problems　of　staircase　effects　and　edge　blurring,　an　improved　fourth-order　partial　differential　equation　image　denoising　model　was　proposed.　The　proposed　model　employed　the　determinant　and　the　trace　of　the　structure　tensor　of　the　image　as　the　edge　detection　factor　and　estimated　the　edge　and　gradient　directions　by　using　the　eigenvectors　of　the　structure　tensor　matrix.　In　flat　regions　of　image,　isotropic　diffusion　is　performed;　in　the　edges　of　image,　the　diffusion　is　along　the　edge　direction;　in　the　corners　of　image,　the　diffusion　is　totally　stopped,　so　the　proposed　model　achieved　anisotropic　diffusion.　Comparisons　results　of　some　relevant　models　in　terms　of　subjective　vision　and　objective　evaluation　index　demonstrate　the　proposed　model　performs　more　effectively　in　removing　noise,　preserving　edge　details　and　avoiding　staircase　effects.　©　2018,　The　Press　of　NUC.　All　right　reserved.