The domestic PTFE hydrophobic membranes were employed in the brackish water desalination experiment by multi parallel type air-gap membrane distillation, using tap-water and Salt solution as testing solution. The desalination performances of membranes were compared. Simultaneously, the effects of the temperature, flow and concentration of the feed solution on the flux of MD processes, the stability of membrane flux, membrane fouling were studied. The results show that the flux and conductivity of membrane 4 # are stable in the tap water and salt water experiments for long-term, especially in the later experiments, the flux of membrane 4 # is the largest .The flux of the membrane 1# which has larger aperture and thinner coating is larger in previous experiments, but the flux decline with the running time, especially in the salt water experiments, the rejection of inorganic salt solutes is low, and the conductivity is high, so it is not suitable for using in brackish water desalination. On the whole, the performance of the membrane 4 # is better. The membrane fouling is serious after the experiment, yellow sediment can be found on the membrane surface.