Robotic belt grinding has higher cutting efficiency and surface quality. However, implicit local contact status makes it is difficult to guarantee processing accuracy and hinders its application in high-end industries, especially when the workpiece has complex contour. And the current local contact status computing methods are inefficient and cannot meet timeliness requirements. Therefore, after analyzing results of FEM and BEM in computing the local contact status, this paper acquires the contact width on abrasive belt based on machine vision. Then the contact width is used as the boundary condition of BEM. Finally, this paper has achieved the contact status fast calculation of the point cloud within 18 mm×18 mm area with the accuracy of 0.2 mm and in 1 s. Compared with FEM calculation results, the maximum error of the contact status obtained by the novel method is no more than 5.6%.