In this paper, a mechanical compression heat pump was coupled into the water-heated humidification dehumidification (HDH) desalination system, in which the condenser is applied to heat the seawater while the evaporator is considered to recover the carried heat from the discharged brine. In view of the integration mechanisms between the desalination unit and heat pump, mathematical models based on mass and energy equilibrium are built. Performance of the combined system, including the water production and gained-output ratio (GOR), at the design conditions are first obtained. Moreover, the relevant influences from the prescribed critical parameters on the performance of the desalination system are simulated and analyzed. The simulation results show that the best performance of the coupled HDH desalination system, appearing as 82.12 kgh(-1) for the water production and 5.14 for the GOR, is acquired at the balance condition of the dehumidifier. Two fully coupled cases, in which the heater or cooler is no longer required, when the air mass flow rate is located at 0.17 kgs(-1) and 0.35 kgs(-1), are found. During the influence analysis, a best value of pressure ratio, PR = 4, is found due to a highest value of GOR as 5.14 although the relevant value of water production is attained as 106.53 kgh(-1) when the pressure ratio is fixed at 5. Furthermore, it is also observed that a lower value of the pinch temperature difference for the condenser, higher values of effectiveness both for the humidification and dehumidification, are effective to elevate the water production and the corresponding thermal efficiency.