Frost build-up on the fins of the evaporator severely decreases heat transfer and subsequently reduces the performance of the heat pump system. In this paper, a novel frost-free air source heat pump system is proposed, which combines with liquid desiccant dehumidification and closed-circuit regeneration. A test setup for investigating the performance of the proposed system and the corresponding performance indexes are developed to evaluate the system performance under variable working conditions. The effects of key parameters including solution temperature, solution concentration, air flow rate and solution flow rate on the regeneration performance and heating performance of the system are analyzed experimentally. Results show that the optimal mass flow rate ratio of the solution to the air is 1.4 in the regeneration mode, while the ratio of 0.55 is recommended in the heating mode. Additionally, performance comparison between the proposed system and the conventional reverse-cycle defrosting system available in the literature is conducted. It is concluded that the proposed system is superior to the reverse-cycle defrosting system when the ambient temperature is less than 0 degrees C and the relative humidity is higher than 65%.