A heat recovery and tandem desalination system using a Fresnel concentrator based on the humidification and dehumidification (HDH) process was investigated experimentally in this paper. In order to test these concentrators in the brackish water desalination field, we designed and built a small solar desalination unit equipped with a curved Fresnel lens concentrator in our laboratory. The sketch and principle of a four-stage multi-effect solar HDH desalination process are presented. The system obtained fresh water by a three-stage isothermal heating mode and the experimental results were compared with those calculated theoretically. The maximum yield of the unit reached 3.4 kg/h and the maximum gained output ratio (GOR) of the system reached about 2.1. These results indicated that the design of our unit needed to be improved with special emphasis on a larger Fresnel lens concentrator.