Based on the machine vision technique, a method for measuring the three-dimensional parameters of plane grinding surface roughness is put forward for fast and on-line roughness measurement on plane grinding surface. In this method, the plane grinding surface image with Ra ranging from 0.1 to 1.6 μm is acquired by CCD and stored in the computer. Firstly, the mid-value filtering, the edge strengthen and the image binary conversion are used to pre-processing the image, and then the values of plane grinding surface roughness are got through characteristic acquisition. It is proved by the initial experiment that the three-dimentional evaluation method put forward in the paper is feasible. When incident intensity is between 0.7×104～1.3×104 lux, incident angle is between 30° and 50°, root mean square value decreases with the increment of Ra. When incident angle is around 30° and Ra>0.3 μm, the kurtosis and Ra have good correlation; When incident angle is 50° and Ra>0.4 μm, the kurtosis and Ra also have good correlation.