The aim of this study is to analyze numerically a multistage pump with some new approaches and compare the results with experimental data. A centrifugal pump, consisting of six backward curved blades, ten vane diffusers and two stages, was used. First, models of an impeller, a diffuser, suction and discharge sections of the centrifugal pump were separately designed by empirical equations. The flow volume of the pump was numerically solved by different turbulence models. Thus, the most accurate results in comparison with experimental data were obtained for the realizable k-ε turbulence model. For the purposes of this study, the effect of balance holes and leakages (clearances) on the performance was scrutinized. In most studies, it is not taken into consideration in computational fluid dynamics (CFD) analyses due to the difficulty of meshing these regions. The experimental studies were performed at a computer controlled pump test rig that was established according to the standard TS EN ISO 9906. The results of CFD/experimental analyses for the pump head, hydraulic efficiency and hydraulic power on the design point, having the flow rate of 80 m3/h and the revolution of 2,975 rpm, were found to be 81.47/80.70 m, 51.98%/51.42% and 17.94/17.77 kW, respectively. The obtained CFD and experimental results were found to be close agreement for the design flow rate as well as for all tested flow rates. Other characteristics of the pump such as velocity, static pressure, streamline patterns and turbulence kinetic energy were also investigated. In addition, the leakages and balance holes have significantly affected the pump characteristics, which must be considered in CFD analyses in order to find more precise results for true-to-life simulations.