The paper analyzes common methods for the optimal scheduling modeling problem of variable-pressure variable-flow operation of inverter-drive pumps connected in parallel and compares the merits and defects of them. In the common method, the objective function is the shaft horsepower of the pumps and the constrained conditions are water supply target and high-efficiency area of pumps. In another method, the objective function is the square of the difference between the actual and needed flow when satisfying the lift target and the constrained conditions are high-efficiency areas of pumps. The paper proposes a new modeling method, which is compatible with the actual operation and has higher precision and satisfies the engineering requirement on lower switching frequency. Simulation results have proved its validity.