As the pivotal component, separators play the important role in electrochemical performance and even determine the safety of batteries to a great extent. Here, a kind of modified polyacrylonitrile/silica-aerogel (M-PSA) as high-safety separator for lithium/sodium-ion battery is reported, which is obtained as follows: the polyacrylonitrile (PAN) nonwoven prepared through electrospinning, is modified by hydrolysis of its nitrile group and then, in-situ growth of silica-aerogel on it. The as-synthesized M-PSA can enhance the chemical stability in conventional electrolytes, such as ethylene carbonate/propylene carbonate (EC/PC), ethylene carbonate/methyl-carbonate (EC/DMC) and diglyme. It shows high porosity and excellent affinity to these conventional electrolytes. More importantly, the M-PSA separator could hold its structural integrity at 250 degrees C and no severe shrinkage at 350 degrees C (80.06% of separator area retention) indicating excellent thermal stability. Electrochemical measurements of the M-PSA separator are tested in lithium battery and sodium battery (half cells and full cells), respectively, exhibiting good cycle performance and fast kinetics. The M-PSA separator is promising as high-safety separator for advanced lithium/sodium-ion batteries for widely applications.