The characteristics across flow vacuum membrane distillation under different operation conditions and the comparison of different membranes under the same operation condition are studied for better understanding of the novel vacuum membrane a distillation process. Different membranes exhibit the same characteristics. The permeate flux versus teed linear velocity and teed inlet temperature are right opening growth parabola and up opening growth parabola, respectively. An important transition region of feed linear velocity which is in the range of 100-250 cm/min at any feed inlet temperature and vacuum pressure is observed in the permeate flux curves. A transition region between 65 degrees C and 70 degrees C of feed inlet temperature at the vacuum pressure of 0.09 MPa is also observed in the permeate flux curves. The permeate flux versus vacuum pressure is the linear growth line. Temperature polarization is intensified with feed linear velocity and feed inlet temperature. The vapor produced in vacuum membrane distillation process is almost saturated vapor. (C) 2015 Elsevier B.V All rights reserved.