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In order to improve the efficiency and head of a centrifugal pump with low-specifc-speed under design flow rate, an optimization approach of performance of the low-specific-speed centrifugal pump of IS50-32-160 was proposed by combining numerical simulation, design of experiment, approximation model and genetic algorithm. Three geometrical parameters containing blade outlet width, blade outlet angle, and blade warp angle were chosen as the design variables, and then 20 impellers were designed by Optimal Latin Hypercube Sampling method (OLHS). Commercial software ANSYS CFX 14.5 was used to conduct the steady numerical simulation to calculate the head and efficiency under design condition, which were chosen as the optimal objectives. Approximation model was built by using the Kriging model between the objectives and design variables, and had good prediction accuracy with R-square values of 0.9513 for efficiency and 0.9294 for head. Finally, the best combination of impeller parameters was obtained by solving the approximation model with genetic algorithm. To demonstrate the improvement of performance, the velocity distribution obtained by steady simulation and the pressure fluctuation intensity distributions calculated by unsteady simulation were compared. The results showed that the performance curves obtained by experiment and numerical simulation had a good agreement and the head deviation under design flow rate was 3.3%. The optimization improved the hydraulic efficiency by 3.2%, while, the head did not improve, but it still met the requirement of design. Compared with the parameters of original impeller, the blade outlet width of optimized impeller was smaller, the blade wrap angle was larger and the blade outlet angle did not change. The optimized impeller was redesigned with the optimal parameters, and the performance was calculated. It can be found that the predicted head and efficiency deviations were 3.3% and 0.056%, respectively. The internal velocity flow characteristics in the optimal impeller were improved and the area of the vortexes in the optimized impeller was smaller. The main frequency of fluctuation of efficiency is 145 Hz determined by blade passage frequency. The fluctuation values of efficiency of original and optimized pump under main frequency were 5.13 and 3.61, respectively. The pressure fluctuation intensity was the lowest at the leading edge of impeller and increase gradually along with the passage. The biggest pressure fluctuation intensity was distributed at the pressure side near to the trailing edge. The area of largest pressure fluctuation intensity was smaller in optimized impeller than in original one. The pressure fluctuation intensity was large from the tongue to the second section of volute, while the pressure fluctuation intensity was small at the seventh and eighth sections of volute. The pressure fluctuation intensity in the tongue reduced in the optimized pump. The pressure fluctuation of the monitor set in the tongue is periodic and there are 6 peaks in one period. The pressure fluctuation coefficient of the monitor in the optimized pump is 0.01, lower than that in the original one. The optimization decreased the fluctuation caused by impeller-volute interaction, thus enhancing the operation reliability of centrifugal pump. The optimization method presented can provide references to the optimization of high efficiency and non-over-load design of low-specific-speed centrifugal pump. [ABSTRACT FROM AUTHOR]