This paper proposes and discusses a new set-up for realtime measurement of surface roughness by correlation of laser speckle patterns. The rough surface is illuminated simultaneously by two plane waves which are obtained from a laser after angular spliting by a biprism. Selecting a small angle of biprism and small angle of incidence, the measurement of roughness covers a dynamic range of 1μm. Finally, the experimental results thus obtained are compared with metrologioal measurement by TALYSURF-5, the agreement of the data is well.