Polynanocrystalline yttria-stabilized zirconia (YSZ) nanofibrous membranes with robust flexibility and heat resistant were fabricated by a combination of electrospinning and heat-treatment process. The morphology and crystallographic structure of YSZ nanofibrous membranes were revealed and regulated by varying polymer composition in precursor solutions, which resulting in an effective control of mechanical properties from brittleness to robust tensile strength of 5.04 MPa. In addition, the relationship between the precursor composition and grain size is deeply discussed during the calcination process. Meanwhile, an inverse Hall-Petch effect of nanocrystalline materials was displayed on the YSZ nanofibrous membranes, due to the abundantly existence of ribbons. Furthermore, the flexible YSZ nanofibrous membranes with excellent bending resistance of 400 times and heat resistance of 1473 K exhibit high filtration efficiency of 99.996% for NaCl particles in the size range 300-500 nm, which suggested them to be promising candidate for high-temperature filtration fields including metallurgy, steel, electric power, incineration, cement industries, etc.