The present invention discloses a selenium-doped nano-silica sol capable of both inhibiting the absorption and accumulation of heavy metal in rice and producing a selenium-rich rice, and a preparation method thereof. The selenium-doped nano-silica sol of the present invention is prepared mainly by using a nano-silica sol as a carrier, sodium selenite and the like as a raw material, vitamin C and the like as a reducing agent, and polyvinylpyrrolidone and the like as an emulsifier, and doping and dispersing selenium in a specific ratio in a silica sol so as to form a selenium-doped nano-silica sol with a special structure and function. The selenium-doped nano-silica sol prepared according to the invention has high stability and high concentration, and is uniform and transparent, and has a silica content of up to 20% or more, a selenium content of up to 1% or more, and low impurity content. The selenium-doped nano-silica sol of the present invention has a pH close to neutral, wherein selenium, in a nano particle
