Co-Fe alloy thin films with high magnetization are desirable in numerous applications. Co-Fe thin films prepared by solution methods with refined microstructures have not been achieved up to now. Here, high magnetic field annealing (HMFA) is introduced for the preparation of Co70Fe30 alloy thin films. The effects of HMFA on their microstructures and room temperature magnetic properties are investigated. The thickness of the derived Co70Fe30 thin films is dramatically decreased from a value of 590 nm without HMFA to 320 nm with 7 T magnetic field annealing, and the refinement of microstructures is also observed with HMFA. The derived Co70Fe30 film annealed under 7 T magnetic field exhibits a saturation magnetization of similar to 2.43 T, close to the theoretical value of 2.45 T. Overall, HMFA provides a feasible way to fabricate larger-area and denser Co-Fe thin films with excellent magnetic properties. (C) 2017 Elsevier B.V. All rights reserved.