In this study, a detailed modeling applicable for membrane dehumidifying system is proposed. This system contains a membrane module, 2-stage vacuum pumps, a condenser, and a regulating valve. The proposed model does not need any prior setting of the vacuum level of the permeate side, and the predictive results are in line with the benchmark. It is found that the COP (coefficient of performance) is 55% higher while the EF (energy factor) is almost 150% higher than the conventional one having the same dehumidifying capacity. For inlet with a fixed relative humidity, both COP and EF are increasd gradually when raising the inlet temperature. Yet the COP and EF reaches the peak values of 5.29 and 6.80 kg/kWh, respectively at a dry bulb temperature near 25.6 °C. Once surpassing this threshold temperature, a pronounced flip-over is seen for both COP and EF. The optimal COP can be obtained by simultaneously adjusting volumetric flowrate and condenser size rather than only adjusting each one individually.