[Objective] To monitor the slow/slight change in the loess plateau hilly region in the operation of silt dam and to detect the risk of dam breach in time by 3D laser scanning technology, to provide the bases for scientific monitoring of the silt dam engineering and for safety evaluation in the Middle Gansu loess hilly and gully area, and for silt dams safety in Northwest Loess Plateau as well.[Methods] The settlement, horizontal displacement and surface erosion of Nanwan and Bieduchuan backbone dam were termly scanned by Nove MS 50. The dam and river irregular shape were recorded by equally spaced point cloud and the deformation of silt dam body was analyzed accordingly.[Results] The comparison of two-stage monitoring results showed that there were 1 cm around changes near the road surface in Nanwan backbone dam map, and an obvious change also was found on the left reservoir bank. The change was about 0.8 cm, which might potentially resulted to small-scale collapses. In half year duration, Bieduchuan backbone dam had an about 1~2 cm decline in the right part. Our monitoring results were consistent with the routine monitoring results from the management department.[Conclusion] The accurate, comprehensive, intuitive monitoring data of dam and bank surface obtained timely from 3D laser scanning technology can make the deformation monitoring work more comprehensive, convenient and credible.