Based on the monitoring net of soil and water conservation at Gaoquan gully small watershed, the relation between natural factors and man-made factor,the laws of time and spacial variation ,the generalized coupling model of sediment at small watersheds were studied systemati-cally,and the mathematic model was established .The results show that the contributing ratio of man-made factor to runoff and sediment reduction was 79.11%, and that of natural factors was 85.69%.The laws of time and spacial variation of loess anti-erodibility and erodibility,and the effects of different indexes on runoff and sediment yield were analysed,the mathematic model on relation between vegetation and soil erosion was also established.According to the generalized coupling model,the effect of“two periods” harness was analysed and evaluated.