Four kinds of mesoporous silica with different pore size distribution were prepared by sol-gel method by using the tetraethyl orthosilicate as silica source,by adjusting the pH and temperature of the synthesis system to control the hydrolysis and condensation process of tetraethyl orthosilicate.The physicochemical properties of silica were characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM）,N₂ adsorption desorption,program temperaturerise desorption （NH₃-TPD）,Fourier infrared spectroscopy（FTIR） and thermal gravity（TG） technology.The alkane/olefin adsorption/separa-tion properties of four kinds of silica were investigated.The results showed that the hydroxyl groups of mesoporous silica were mainly free hydroxyl groups.With the increase of synthetic end point pH,silica gel′s pore volume and pore size increased,the specific surface area,the concentration of silicon hydroxyl and the acid content decreased,the acid intensity increased.The pore size distribution and acid properties had obvious influence on adsorption and separation performance.The samples with average pore size of 4.9 nm had suitable acid intensity,the separation degree ofR_{alkane/olefin} was above 1,the desorption rate of alkene was fast,with the ratio of absorption/desorption rate close to 1,which was found to be an ideal adsorbent for alkane/olefin separation.