Based on the spectral-speckle correlation method with ensemble average, dichromatic digital speckle correlation method is introduced to measure the surface roughness. The properties of dichromatic speckle spatial correlation parameter are investigated through simulated speckle fields. And the location relation of sample and target areas is also studied. Window size influence in digital image process on peak value of spatial correlation is experimentally discussed. The surface roughness of blasted-shot and grinding specimen is measured. It is shown that dichromatic speckle spatial correlation parameter can describe surface roughness effectively. The new method has the virtue of fast image acquisition and good stability.