In spite of the great promise of pervaporation (PV) in production of fresh water from salty water, major challenge still lies in the developments of PV membranes with high water flux to compete reverse osmosis membranes. Here, we fabricated composite PV membranes consisting of a porous polyacrylonitrile (PAN) substrate and a dense selective layer of polyvinyl alcohol (PVA) crosslinked by 4-sulfophthalic acid (SPTA) of which sulfonic acid groups acted as facilitate transport agents to water molecules. Effects of the SPTA concentration and thickness of the PVA layer to the desalination performance were studied at temperatures from 30 to 70 degrees C and NaCl concentrations up to 100,000 ppm. A high water flux of 46.3 kg/(m(2).h) with a salt rejection of 99.8% was achieved when separating a 35,000 ppm NaCl solutions at 70 degrees C. However, water permeance only increased 5.3 times as the PVA layer thickness decreased 95 times (from 76 mu m to 800 nm). Our study showed that water permeability of the PVA layer significantly decreased with thickness of the PVA layer. This phenomenon indicated that a thin and dried region close to the downstream side of the PVA layer governed the water transport property.