High magnetic fields (HMF) can pass high intensity energies to the atomic scale of materials without contact to change the thermodynamic state of materials, and affect the arrangement, matching and migration of atoms and molecules. Therefore, in this work, HMF was introduced into wet-chemical synthesis to prepared FePtCu nanoparticles (NPs). The results show that the FePtCu NPs with L10 structure, uniform morphology, and good dispersibility were successfully prepared under HMF. The HMF increased the size, ordering degree s and the coercivity of the FePtCu NPs. The L10-FePtCu NPs with sizes of about 11 nm and ordering degree of 0.8985 were obtained under the HMF of 6 T. The HMF might magnetize the NPs and cause lattice distortions, which facilitates formation of vacancies or defects in the FePt NPs. A lot of vacancies are effectively accelerate the orderly diffusion of Fe and Pt atoms, and promoted the disordered-ordered transformation of the FePt NPs. Therefore, HMF assistance can accomplish the regulation of ordered structure. This method offers a new path for the direct synthesis of L10 structured nanomaterials.