Abstract: A large number of warping dams, which have formed lots of dam systems in small watersheds, have been built in the Loess Plateau of China. When the layout of a dam system is inappropriate, breach of one dam usually causes chain failure of the downstream dams. In order to properly evaluate the flood control capacity of a whole warping dam system, a method to simulate the chain breach process of warping dam systems caused by rainstorm is proposed. A grading rule for dams in a system is defined, and a method for automatically determining the grade of each dam is put forward. According to the grade, from low to high, the runoff yield analysis, storage analysis, dam-breach judgment and dam-breach flood analysis are carried out sequentially for each dam to simulate the chain failure process of a dam system. These methods are implemented in a program and is used to simulate the chain breach process of the Wangmaogou warping dam system in Suide County, Shaanxi Province, China, and the results are discussed in comparison with the investigated flood damage in July 2012.