Abstract: In order to study the effective method of arroyos extraction for ephemeral stream in hyper-arid area. Arroyos were extracted automatically in gobi catchment using the hydrological analysis model in ArcGIS platform on the base of DEM, and the author discussed the effect of drainage water threshold on the extracted arroyos by overlapping the TM image to verify the accuracy. The results showed that: the smaller the drainage water threshold, the finer and more concentrated of the extracted arroyos were, while the larger of drainage water threshold results in the sparser of extracted arroyos; as the research area was large, according to the research objectives, when the drainage water threshold reached to the 4.5 km2, the extracted arroyos would better describe the arroyos distribution in gobi catchment, with the better matching up arroyos located in the upper catchment and in the main and sub-main breaches, could meet the practical needs. The fact that there was a turning point on the curve between drainage water threshold and the accumulated numbers of the first sources breaches could be used to roughly determine the best drainage water threshold for arroyos extraction.