A novel Air-Gap Diffusion Distillation (AGDD) technology operated at normal atmospheric pressure was proposed in this paper. In this plant, cold and hot streams flow counter-currently and the strong hydrophilic porous medium is employed as the hot stream channel to control its flow. The operation characteristics of AGDD were investigated and analyzed theoretically and experimentally. Influences of structure and operation parameters on the performances were discussed deeply. The results showed the water productive flux and Gained Output Ratio (GOR) for the AGDD with one air-gap combination were 0.7244 kgm(-2).h(-1) and 1.16 respectively when the thickness and height of air-gap, inlet temperatures of cold and hot streams, mass flow rate of cold stream were 5 mm, 0.9 m, 25 degrees C, 65 degrees C and 4 kg.h(-1) respectively. When the air-gap height was enlarged to 1.8 m and the mass flow rate of cold stream reduced to 2 kg.h(-1), the water productive flux and GOR were 0.5255 kg.m(-2).h(-1) and 5.01 respectively. The results also indicated that the thermal resistance of heat transfer in the AGDD mainly sourced from the air-gap. The variations of structure or operation parameters did not influence on the desalination rate of AGDD which was higher than 99.8% during experiments.