A novel frost-free air source heat pump (ASHP) combined with membrane-based liquid desiccant dehumidification and humidification is proposed and investigated in this paper. Liquid-to-air membrane dehumidifier (LAMD) is employed to dehumidify the air before entering the outdoor coils in the proposed system so that frosting can be prevented. Diluted solution is regenerated to humidify the supply air via the liquid-to-air membrane regenerator (LAMR), which can overcome the droplets carry-over problem in the liquid-to-air energy exchanger. Model simulations are carried out to study the system performance under various operating parameters and climatic conditions, meanwhile the comparison between the proposed system and conventional defrosting system is performed. Results demonstrate that the COPsen and the COPtot of the novel system are at least 37.7% and 64.3% higher than that of the COPreverse of conventional reverse-cycle defrosting ASHP system in the variation ranges of the analyzed parameters,respectively.Humidification effects on the supply air depend on the ambient air properties. And air humidification by the regenerator can meet the needs of the air-conditioning room comfort when the ambient air is above 0 degrees C and 70% RH. (C) 2017 Elsevier B.V. All rights reserved.