The invention discloses a method for determining the bothway flow distributing mixed flow type water pump turbine blade space position. The diameter of inlets and outlets in the related positions of long blades and short blades, the offset positions of the short blades and other parameters are optimized, a runner of a water pump turbine can have the bothway flow distributing function, and therefore the pressure fluctuation of a non-blade area of the water pump turbine is greatly reduced, and the cavitation performance of the inlet of the runner under the water turbine working condition is greatly improved.