Abstract: This paper introduces the flowrate control for frequency and inverter pumps in parallel operation. Varieties in pressure and flowrate for frequency and inverter pumps in separately operation and parallel operation are analyzed. It is pointed out that under the condition of frequency and inverter pumps in parallel operation, controlling the opening of pump valve and rotary speed of inverter pump are needed to ensure stable operating of the whole system. In the light of throttle loss problem existed in controlling the valve opening of inverter pump, impeller improvement for frequency pump is considered as a feasible method.