Small hydropower stations as renewable resources of energy have noticeable potential in the world and with increasing energy demands, using such potentials is a need especially in many developing countries. The major problems of installing the new small hydropower stations are their high specific cost expressed in $/kW installed capacity and maintenance expenses. Part of the solution of these economic problems is to substitute the conventional turbines by simple and inexpensive machines such as reversible pumps. In this present work, an axial pump is simulated in reverse mode by computational fluid dynamics using different turbulence models and Characteristic curves of the reverse pump are obtained for each turbulence model and are compared with experimental data. The results show that Spalart-Allmaras model is preferred for investigation of operation of the axial reverse pump. In the next step, the effects of blades position and impeller size reduction on characteristic curves are considered. The results show that the axial pump can be easily run as a low-head turbine. Also it can be applied in the wide range by combination of blades angle adjustment and impeller size reduction. But the efficiency of turbine mode is low.