A combined approach of inverse method and direct flow analysis is presented for the hydrodynamic design of gas-liquid two-phase flow rotodynamic pump impeller. The geometry of impeller blades is designed for a specified velocity torque distribution by treating the two-phase mixture as a homogeneous fluid under the design condition. The three-dimensional flow in the designed impeller is verified by direct turbulent flow analysis, and the design specification is further modified to optimize the flow distribution. A helical axial pump of high specific speed has been developed. To obtain a favorable pressure distribution the impeller blade was back-loaded at the hub side compared to the tip side. Experimental results demonstrate that the designed pump works in a wide flow rate range until the gas volume fraction increases to over 50% and its optimum hydraulic efficiency reaches to 44.0% when the gas volume fraction of two-phase flow is about 15.6%. The validity of design computation has been proved.