This work studied the preparation of the flat-sheet polyvinylidene fluoride (PVDF) membrane by immersion-precipitation for applying in membrane distillation. The casting dope comprise PVDF, triethyl phosphate and Tween 20.In this work, TEP was selected as solvent, and the effect of TEP concentration(20, 40, and 60, respectively) in the coagulation bath on the morphology of membrane was investigated. In membrane distillation, the performance of air gap membrane distillation (AGMD) and water gap membrane distillation (WGMD) at different feed temperature (50-70 oC), flow rate (0.4-0.8 L/min), gap width (0, 1, 3 mm) was investigated. Finally, the advantages and the disadvantages between DCMD and WGMD was investigated by permeate flux and gained output ratio (GOR). The experimental results indicated that the pore size, porosity and contact angle of membrane became larger and the thickness of skin layer smaller as increase in TEP concentration. The water has higher thermal conductivity than air, thereby the flux of WGMD is higher than AGMD. The flux of membrane distillation increased as the decrease in the gap width and increase the feed temperature and flow rate. The highest flux of WGMD is 31.82 L/m2hr, when the feed temperature is 70 oC, flow rate is 0.8 L/min and the gap width is 0 mm. The results of long-term operation show that the flux of the T60 membrane decrease 4%, and the salt rejection maintain 99.99%. This result represents that the T60 membrane have good stability in long-term operation. In the performance comparison between WGMD and DCMD, although the flux of DCMD is higher than WGMD, the GOR of WGMD is higher than DCMD, which means that WGMD is better than DCMD in energy efficiency.