Abstract: An optical detection technique for rapid measurement of surface roughness by using a laser beam is proposed.When a laser beam illuminate on the surface of a aluminum specimen,the space distribution of the reflected light intensity will be the function of the roughness of the surface of the specimen.And the intensity distribution can be measured with a plasma coupled device (PCD) and approximately expressed with Gaussian function.The broadness of the intensity distribution curve can be evaluated with standard deviation called Gaussian curve parameter (GCP).We find a experimental equation Ra=0.088GCP+0.032 to show the relationship between center line average roughness Ra and GCP in range of 0.1～0.5μm.