The invention discloses an organosilicon nanomaterial CO2 adsorbent with a double-brush structure, and a preparation method thereof. The material mainly comprises an organosilicon nanoparticle material and organic amine loaded on the organosilicon nanoparticle material, the organosilicon nanoparticle material has the double-brush structure, and a long alkyl chain and a silane organic matter jointly act in pore channels of the material, so that the material has good amine stability and dispersion and has an excellent CO2 adsorption capacity. The highest CO2 adsorption capacity of the material is 5.34 mmol/g (the volume fraction of CO2 is 15.1%). In a cycle test, after adsorption-desorption cycle is carried out for 100 times, the adsorption capacity still reaches 5.24 mmol/g, so the adsorbent has a high stability. The material has excellent properties, so that the material has the potential of large-scale industrial application in CO2 adsorption.