PVA nanofibers are generally required to be modified because of its poor stability in water. The water stability of PVA nanofibers was improved by heat treatment in this paper. The DSC test results showed that the crystallinity of heat-treated PVA nanofibers at 150°C for 10 min reached the maximum which increased by 12% compared with PVA nanofibers. From the SEM images it was observed that the heat-treated fibers didn’t dissolve in water but showed certain degree of agglutination and swelling. PVA nanofibers were taken as the inner layer of the sandwich structure purification material prepared with the hot pressing technology. The filtering experiments showed that the filtration properties were better when the area density of PVA nanofibers was 2.5 g/m2.