Abstract: Transient pressure distribution along a pipeline is important to water hammer protection for a long-distance water supply system. Once pump failure occurs the pressure behind the pump drops quickly after pump failure, and a long pipeline will be involved. Using the method of characteristics (MOC) and theoretical analysis, this paper analyzes the propagation of water hammer along the pipeline, and derives a formula for transient pressure decrease along the pipeline. The results show a good agreement of this formula with MOC calculation, and indicate that the pressure drop is diminishing along the pipeline if its wall friction is considered. The formula that takes an explicit form, is more convenient in the design of water hammer protection schemes.