The invention belongs to the field of olefin polymerization catalysts and particularly provides a supported iron catalyst, a preparation method thereof and an iron catalyst system. The supported iron catalyst comprises a manganese chloride/silica gel carrier and an iron single active center component supported by the carrier, wherein a precursor of the iron single active center component is a bis(imino)pyridine Fe (II) complex with a structure as shown in the formula 1, wherein R1-R10 are same or different and are respectively selected from H, halogens or C1-C4 straight-chain or branch-chain alkyls. Compared with a bis(imino)pyridine Fe (II) catalyst which is not modified by manganese chloride, the supported iron catalyst provided by the invention is not only relatively high in polymerization activity, but also capable of keeping the performance of a polymer basically constant when being used for olefin polymerization.