The invention relates to an activated carbon fiber-loaded iron doped titanium dioxide photocatalyst and a preparation method thereof, belonging to photocatalyst and the preparation method thereof. The invention aims at providing the titanium dioxide photocatalyst which is loaded on an activated carbon fiber and is directly combined with iron, and the photocatalyst enables the iron doped titanium and the activated carbon fiber to cooperate with each other to act and has stronger capability of degrading and decomposing organic contaminant and better reusability. The photocatalyst is prepared from the activated carbon fiber to which titania and iron are attached, wherein the content of the iron is 0.01 to 0.15 percent according to mass percent; the preparation method is as follows: preparing colloidal sol containing iron and titanium, attaching the colloidal sol to the activated carbon fiber, and calcinating the activated carbon fiber at the constant temperature ranging from 900 to 950 DEG C; or preparing the colloidal sol into gel, and obtaining the finished product by calcinating the gel. The invention can be used for degrading organic contaminant in wastewater.