Referring to the complicated operating and bad field measuring of existing surface roughness, an on-line measurement method is presented based on laser two-dimensional scattering principle. The method proposed can not only measure the surface roughness parameters, but also figure out the surface topography. In this measurement, by using non-diffraction laser beam as light source and high accuracy CCD camera as displacement sensor, and applying the method of signal processing of surface roughness by Matlab, real-time measurement of surface roughness can be realized. This method is realized with modularized design, and has the advantages of simple structure, powerful real-time processing capability, high-precision measurement, visual display, and easy operation, etc.