The invention discloses a flexible optical film and a preparing method of the flexible optical film. The flexible optical film comprises titanium dioxide and silica gel, wherein the titanium dioxide and the silica gel are mixed according to 0.01% to 20% by weight ratio. The flexible optical film has good elasticity, and therefore folds caused by folding of the flexible optical film can not be produced. Meanwhile, compared with a traditional optical film, the flexible optical film is applied to an organic light emitting diode backlight or illuminating system and has an excellent optical property. The flexible optical film has a better optical property and better optical color rendering when fluorescent powder or phosphorescent powder is further added to the flexible optical film.