The invention relates to an optical film, particularly relates to a novel blue light prevention optical film applied to displays, LED screens or the illumination field and a preparation method thereofand aims to filter out the high energy short-wave blue light which is from the displays and illumination devices and is not good for eyes. The blue light prevention optical film sequentially comprises a functional layer, a base layer, an under-coating layer and a blue light prevention layer, wherein the blue light prevention layer is composed of cholesteric liquid crystal molecules, a chiral agent, a photoinitiator and a polymerization inhibitor. Through controlling the pitch of the cholesteric liquid crystal formed in the blue light prevention layer, the blue light in the 420-460 nm band canbe selectively reflected, and thereby the excellent blue light prevention effect is realized. The novel blue light prevention optical film is advantaged in that not only can the relatively good bluelight prevention effect is realized, but also excellent optical performance such as high brightness and low color deviation is further realized.