The invention provides a method for preparing 
nano porous materials with a large specific surface area by a vacuum 
freeze drying method with short period, simple process and non environmental 
pollution, which comprises the following steps: (1) taking an organosilane presursor or 
metal alkoxide as a 
raw material to synthesize wet gel; (2) allowing the wet gel to stand for 1 to 7 days, and performing aging on the wet gel; (3) using 
ethanol to clean the wet gel for 1 to 2 days; (4) adding a modifier into the wet gel for soakage for 1 to 2 days, performing 
solvent displacement, and modifying a three-dimensional 
network structure of the wet gel; and (5) placing the obtained product into a 
freeze drying box for prefreezing and 
vacuum drying. The method is to adopt a novel 
drying method, namely the vacuum 
freeze drying method, to dry the wet gel on the premise of maintaining the structure of the wet gel. The 
drying method has short period and simple process, avoids environmental 
pollution, cannot damage the 
network structure of the gel, reduces the production cost, and accelerates the large-scale commercialized application process of 
nano porous super heat-insulating materials, catalysts and catalyst carrier materials.