A method for calculating the H-Q, η-Q characteristics of a multistage pump is considered in this paper. The results of the calculation and experiment agree well. A feature of CNS pumps is a small gap between the impeller and diffuser blades. In this case, the non-stationary approach gives the best results. Optimization has been carried out for stator blades, increasing the efficiency of the pump by 3,8 %. The method proposed by Sobol and Stanikov for exploring the parameter space was used in optimization. Calculation of pulsations of radial force has been performed for the pump rotor. The calculation shows that the amplitude of the force decreases with increasing clearance.