Abstract: At present, the calculation of the hydraulic parameter needs select the rheological model so as to compute the circulating pressure drawdown accurately, and it is the basis of design and calculation of bit hydraulic parameter. We think design the hydraulic parameter by adopt Herschell-Bulkley mode is more simple and accurate than Bingham mode and Power law mode. Based on given the exact resolution of circulating pressure drawdown calculated by Herschell-Bulkley mode, the optimum hydraulic route is designed by the foundation of maximum bit hydraulic power working method. And through this selects optimized hydraulic parameters and various nozzle dimensions. Comparing the Herschell-Bulkley mode with Bingham mode and Power law mode by the calculation example and the developed program the calculation results is discussed. The example shows that the design method in this study satisfies drilling engineering needs.