Soil erosion is one of the major factors for land degradation in mountains. Contour hedgerow system, consisting of thickly planted double or single hedgerows of nitrogen-fixing trees or shrubs, shows great potential in soil conservation of cultivated slope lands in the tropics. On-farm research was carried out in Ningnan county of southwest China to assess the effect of hedgerows on soil erosion control in the subtropical region. The research consists of four treatments with three replicates. The results showed that more than 70% soil erosion occurred in the mid-term of monsoon under the traditional cultivation. The 4～7 year old hedgerows of L. leucocephala and T. candida reduced soil loss to be 1%～3% of the control. The erosion is also an accelerating nutrient-loss procedure. The contents of total nitrogen and organic matter in the sediments were more than 2.3 and 2.47 times of those in eroded topsoil. Maintenance of hedgerows can also lead to formation of terrace after normal cultivating in the alleys for several years.