Inspired by conventional powder coating technology, a novel negative-charged membrane made of thin-film nanofibrous composite (TFNC) with polyacrylonitrile (PAN) nanofibers as the substrate and polyvinyl alcohol (PVA)-sodium alginate (SA) as the hydrophilic barrier layer was successfully developed. The PVA-SA nanobeads were firstly electrosprayed onto the electrospun PAN substrate and then hot-pressed under steam humidification. Water molecules were absorbed from the ambient moisture acted as the "plasticizer" in PVA-SA nanobeads, which could facilitate softening or melting of PVA-SA during the film-formation process. The moistened PVA-SA nanobeads layer would then be pressed imperceptibly into an integrated barrier film on the PAN supporting layer under the gravity pressure of hot plate at a certain temperature. Deposition time (the timespan for PVA-SA electrospraying), moist-curing time, heating temperature (the preset temperature for thermal treatment) and curing time (the timespan for thermal treatment) were carefully adjusted to explore the optimal film-formation condition. And it was found that with the deposition time of 18 min, moist-curing time of 120 s, heating temperature of 60 degrees C and curing time of 6 min, an integrated and nonporous PVA-SA barrier layer was achieved for TFNC membrane. Finally, the resulting barrier layer was chemically crosslinked by glutaraldehyde (GA) and its compactness could be easily controlled via different crosslinking degree and the composition of crosslinking bath for nanofiltration (NF) applications. The optimized PVA-SA/PAN TFNC membrane (crosslinked by GA with concentration of 0.4 wt%) was negatively charged owing to the carboxyl groups of SA, and it possessed high NF performance in anionic dye filtration. Tests at low feeding pressure of 0.6 MPa showed a permeate flux of 57.1 L/(m(2) h) and rejection ratio above 96.8% for the membrane product toward Acid Blue 90 solutions. Besides, the resultant PVA-SA/PAN TFNC membrane exhibited excellent pressure resistance and antifouling properties during the long-term experiment, and the negatively charged SA played a key role in the NT process.