Abstract: In order to solve the problems of manual intervention and long testing time existed in using contact method to test surface roughness, a fast testing method and an instrument for surface roughness were proposed. Base on laser triangle principle, laser was projected onto the testing object and the image of reflected light was received by camera, and the 3D coordinate of measurement area through the image processing algorithms and coordinate transformation was obtained, and then the parameter results of the earth’s roughness were obtained on the basis of the roughness computing formula. Also, field experiments and precision experiment were conducted with this instrument. The maximum of average comparative error for measurement result was 2.93% through precision experiment. The instrument's typical resolution level was 0.78, 1 and 0.83 mm, in the scanning's vertical direction, in the scanning and in the earth's vertical direction, respectively. The experimental results showed that the spatial autocorrelation coefficient of soil surface can express row structural characteristic of furrowed soil, which verified the feasibility and availability of the instruments and methods proposed in this paper.