Abstract: Abstract: Global energy issues affect the economic development, it is the base of improving national standard of living conditions. According to incomplete statistics, power consumption of pumps account approximately 17% of total generating capacity. Thereby increasing the efficiency of the pump is necessary to energy conservation which also has a very important significance on creating a resource-saving society. Mixed-flow pumps are more and more widely applied to industrial and agricultural production, the requirement of the performance of the mixed-flow pump become increasingly high. When the working condition deviates from the designed condition, the flow filed at impeller outlet does not match well with the flow field at volute inlet, which will lead to the efficiency drop of mixed-flow pump. Reasonable design of mixed-flow pump impeller and volute can improve the distribution of flow field, and then improve the hydraulic performance of the mixed-flow pump. Based on theoretical analysis, numerical simulation and model experiment research methods, impeller and volute matching optimization of high specific mixed-flow pump with volute were conducted. This paper developed a high-performance mixed-flow pump model with double volutes whose ns equals to 585 with the target of perfect match between impeller and volute under different flow rate conditions. The full three-dimensional numerical calculation internal flow field and radial force of the optimal designed high specific speed mixed-flow pump with double volutes was investigated. Numerical simulation of the pump used the standard κ-ε turbulence model. The κ-ε turbulence model was considered to be a model which can predict the hydraulic performance and simulate the internal flow field accurately. The calculation domain contains inlet pipe, runner, volute, outlet pipe. And the mesh of inlet pipe and outlet pipe adopted unstructured mesh, the mesh of runner and volute adopted unstructured mesh. The results of numerical simulation were in agreement with the experimental ones, which indicated that the numerical simulation model and the calculation methods could be used to predict the internal-flow in a double volutes mixed-flow pump. The results showed that: the high efficiency area in the double-volutes pump was significantly broadened compared with the single-volute pump. And the internal flow streamline was very smooth at working condition in the double volutes mixed-flow pump. The pressure distribution in the double volutes pump revealed a increasing trend from impeller inlet from inlet outlet, which could make the impeller do work to the fluid effectively. the efficiency of double-volutes pump at designed flow rate was higher than the single-volute pump; the radial force in the double-volute pump was also smaller than the single-volute pump, which indicated that the double-volutes program not only keeped superior hydraulic performance but also could significantly reduce the radial force in comparison with the single-volute program; The radial force vector trail always presented a square distribution and the radial force fluctuation was always regularly, which contains 4 crests and 4 troughs in one rotating period. The conclusion in this paper had reference value for the design and study of internal flow in the mixed-flow pump.