The hydrodynamic properties of the blade aerofoil differ from that of the airfoil of the blade cascade in a pump of low head. The numerical simulation of the flow quality in the impeller was made on a commercial axial pump of low head. The blade cascade flow in impeller was discussed, and the characteristic of the airfoil profile of the impeller blade was studied using the FLUENT software. The characteristic of the isolation aerofoil was compared with that of the aerofoil of impeller blade cascade. The research results show that the pressure on the surface of the aerofoil of blade cascade is higher than that of the corresponding isolation aerofoil, under the designed work conditions, at the same angle and the same place. On the same aerofoil, the change of pressure of aerofoil of the blade cascade is less than the pressure of the isolation aerofoil on high pressure side, but it was opposite on low pressure side.