In order to further satisfy the operation needs for social applications, a shaft-less double suction mini turbo pump with outer impeller diameter of 24 mm and specific speed of 188 min-1·m3min-1·m has been designed. In order to simulate the three dimensional steady turbulent flow in the mini pump so as to improve the pump impeller design, RANS equations and k-ω SST turbulence model are used. Based on the detailed analysis of the internal flow in the pump, six new impellers have been designed to investigate the effects of impeller parameters on the performance of the mini pump. Based on those results, the following conclusions are drawn: (1) For the double-suction shaft-less mini turbo pump, the averaged wall shear stress has very low level and the maximum hydraulic efficiency is larger than 80%. Those favourable features must be related to the symmetric suction design of the mini pump; (2) Large vane angle at the trailing edge is suitable for a mini turbo pump in many applications so as to obtain higher head and smaller impeller size. On the other hand, the impellers with β ₁=90° may result in large wall shear stress at the vane leading edge at small flow rate; (3) Because the radial impeller is much convenient for manufacture and creates much larger head, it is preferable for a mini turbo pump if the wall shear stress can be controlled within the acceptable range due to further design optimization.