Gully density is an index to evaluate gully erosion and describe the sketch of gully erosion in a watershed.At present,some different approaches,such as grid approach and small spot number approach etc.,are used to investigate the gully density.However,there is no unique approach to be used by different investigators.Although these methods mentioned above can describe the existing condition of the gully erosion in a small watershed,it can not provide the antecedent information for the design of gully harnessing engineering.Nevertheless,the hydrological network approach,which can divide a large watershed into several sub-watersheds according to the gully characteristics,can give the same result of gully density in a watershed as the other approaches by combining investigation of engineering layout.Additionally,the basic data gained by using the hydrological network approach are in preparation for the later design of gully harnessing engineering,which can be used anytime.