Abstract: Based on the rainfall-runoff observations under the natural rainfall at the Gaolan Research Station of Ecology and Agriculture, Cold and Arid Regions Environmental and Engineering Research Institute, CAS, in 1998-1999, the threshold rainfall values for 9 rainfall-harvesting catchments were determined by the linear regression model.The results indicated that: (1) the threshold rainfalls were 8.5mm, 8.0mm and 4.0mm under the no effect of the antecedent rainfall for the natural loess slope catchment, slope clearing catchment and compacted clay catchment, respectively, and (2) the threshold rainfalls were 6mm, 5.0mm and 1.9mm under the effect of the antecedent rainfall conditions, respectively.The threshold rainfall for the plastic film, the asphalt felt, the asphalt sprayed cat chment, the ‘big' pebble covered (7-14 cm in diameter) film and the "small" pebble-covered (2-6 cm in diameter) film catchments were 0.13mm, 0.21mm, 0.17mm, 0.98mm and 0.85mm, respectively.The threshold rainfall for the concrete cat chments is 1.48mm without the effect of the antecedent rainfall effect and 1.16mm with the antecedent rainfall effect.