Creating a desirable porous membrane with high-flux and energy-saving properties for the purification of water containing submicron-sized contaminants, especially pathogenic microbes, is of great significance, yet a great challenge. Herein, we demonstrate a facile methodology to construct an innovative membrane with continuous cellulose Voronoi-nanonet structures via nonsolvent-induced phase separation. This approach enables cellulose Voronoi nanonets to tightly weld with electrospun nanofibrous substrates by controlling the solvent-nonsolvent mutual diffusion process. The resultant membranes exhibit integrated properties of small pore size (0.23 mu m), high porosity (90.7%), good interconnectivity, and ultrathin thickness (similar to 600 nm, 2 orders of magnitude thinner than the conventional microfiltration membrane). As a result, the prepared membranes can effectively intercept submicron particles (similar to 0.3 mu m) with robust rejection efficiency (>99.80%) and ultrahigh permeation flux (maximum of 8834 L m(-2) h(-1)) under an extremely low driving pressure (<= 20 kPa). More importantly, prominent bacterial rejection efficiency with a log reduction value (LRV) of 8.0 (overcoming the previous limitation of LRV <7) and outstanding antifouling function are also achieved for the membranes. The successful fabrication of such a versatile membrane may provide new insights into the development of next-generation high-performance separation materials for various applications.