Abstract: The brokenline practical weir as a low weir is being widely used in many middle and small scale water conservancy projects.The paper describes the research results on this weir's discharge capacity.On the basis of summing up the previous research results and through analyzing experimental data,authors proposed a limitation for applying a brokenline practical weir(namely,the ratios of weircrest width to head above weir are more than 0.67 but equal or less than 1.5～2.0, ratios of weir height to head above weir are equal or more than 0.5;the upstream slope of this kind of weir is about 2.0),and gave the formulas for calculating discharge coefficients under free overflow condition. 