Abstract: The drag reducing action is the way of injecting small amount of drag reducing agent into the fluid. So that is a phenomenon of increasing throughput. The paper introduces some experimental formulas for the prediction of drag reducing rate and obtaing the compond experiential formulas among DR (drag reducing rate), Re (Reynolds number), PPM (concentration) and ID (pipe diameter) based on the typical data of drag reducing experiment. This formula may be used to evaluate and predict drag reducing rate of enlarged pipe diameter for the same system of drag reducing agent and solvent within the range of less varied tempre ture and viscosity based on the experimental data of two smaller inside diameter pipos.