Abstract: The traditional algorithms for friction loss in transient flow are improved to solve their low computational precision.It is put forward that dynamic friction coefficient (or factor) is used to calculate transient friction and integral item of friction loss is treated by Simpson method,which can improve calculating precision.The computational sample is shown that,on the premise of the same precision with traditional algorithms,the method proposed by the paper can reduce computational load remarkably and save calculation time in the application of water hammer analysis in long distance pipelines.