In order to optimize the inner flow of the regenerative pump used in gasoline injection systems, we carry out experimental and numerical flow investigations.A qualitative analysis of spatial flow phenomena in selected regions of the pump is presented by employing the laser light sheet technique. Therefore, a tenfold enlarged water model is built up, where dynamic similarity with the original flow is achieved. The results of the flow analysis have led to improved geometries which are compared with the original design by measured pump characteristic curves.Furthermore, three-dimensional simulations of the fully developed turbulent flow using a finite-element method are presented. The flow with respect to the rotating impeller is calculated by solving the Reynolds equations in connection with the k-ε-turbulence model. After verifying the numerical results with experimental data the quantitative influence of a selected geometrical parameter, i.e. the vane angle, at various operating points is simulated and discussed. The good agreement with experimental measurements shows that the numerical model is reliable to judge geometrical parameters regarding their influences on the pump performance.