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The pumpturbine unit is one of the most important component of pumpedstorage power station. The axial force characteristics on pumpturbines runner is very important and may strongly influence the stability and security during the common operations. As a typical verticalaxis pumpturbine unit, some reasonable downward axial force is very necessary to load on the runner for preventing the entire pumpturbine unit from unitlifting. However, this downward axial force may be too large in magnitude especially in its pump mode. The large downward axial force will be the reason that inducing the undesirable unitsinking phenomenon. In the current investigation, a prototype pumpturbine unit was specifically studied based on the computational fluid dynamics method. The axial force was analyzed under different flow rate conditions and also different guide vane opening angle conditions. Results showed that the downward axial force met the maximum value under small flow rate condition, small guide vane opening angle condition and high head condition. The pressurebalance pipe can be applied to connect the runner upper crown leakage and the draft tube. The pressurebalance pipe can solve the problem of overloaded downward axial force. The axial force characteristics in pump mode became slightly upward without obvious change on the head and the hydraulic efficiency of pumpturbine unit. Thus, the operation stability and security of pumpturbine unit can be obviously enhanced.