Abstract: Based on the analysis of pervious work about Coal Water Slurry (CWS), this paper considered the varying of flow velocity distribution inside pipe caused by the yield stress of CWS, analysed the pipe flow of CWS theoritically and proposed a theoritical calculating method of pipe flow drag of CWS. Also, a lot of experiments have been carried out to identify the method. The experimental results correspond to the theoritical analysis very well. This calculating method can be applied to the disign of practical engineering of CWS.