To solve the problem of reduced energy efficiency in some working conditions due to the need for an extra heat source in desiccant wheel-assisted pre-humidification air water harvesting systems, this paper proposes an air water harvesting device combining a two-stage desiccant wheel and a heat pump, builds a numerical simulation model, and studies its optimal air treatment process and water harvesting performance under various climates. It first analyzes water production, water harvesting efficiency (ewh) and other parameters under two extreme conditions: extremely humid-cold (5 oC, specific humidity 4.88 g/kg, 90% RH, RH for relative humidity) and extremely dry-hot (46 oC, specific humidity 6.29 g/kg, 10% RH, RH for relative humidity). Results show the unit achieves the target daily water production of 12.5 L/d under both conditions, with ewh of 2.40 kg/(kW·h) and 1.49 kg/(kW·h) respectively. Heat recovery effectively cuts compressor power under the dry-hot condition, but shows little energy-saving effect under the humid-cold condition. Taking monthly average temperature and humidity in Kashi, Xinjiang as typical conditions, this paper further evaluates unit performance with and without heat recovery. Daily water production meets the target from March to November, and reaches 49.6%–82.4% of the target in January, February and December. With heat recovery, compressor power drops by 2.9%–50.6%, and ewh rises by 3.2%–101.9%.