Motivated by the impressive effect of the SUSAN operator for low level image processing and its usage simplicity, we extend it to denoise the 3D mesh. We use the angle between the normals on the surface to determine the SUSAN area; each point has associated itself with the SUSAN area that is has a similar continuity feature to the point. The SUSAN area avoids the feature to be taken as noise effectively, so the SUSAN operator gives the maximal number of suitable neighbors with which to take an average, whilst no neighbors from unrelated regions are involved. Thus, the entire structure can be preserved. We also extend the SUSAN operator to two-ring neighbors by a squared umbrella-operator to improve the surface smoothness with little loss of detailed features. Details of the SUSAN structure preserving noise reduction algorithm are discussed along with the test results in this paper.