Rationally regulating compositions and atomic arrangements is essential to tune the geometric and electronic structures of Pt alloy nanoparticles (NPs), thus largely optimizing their electrocatalytic performance towards methanol oxidation reaction (MOR). Herein, we present a facile alloying-ordering strategy to directly convert pure Pt NPs into size-controlled PtFe ordered intermetallic NPs by virtue of thermal interdiffusions under an easily-removable NaCl cover. And the disordered counterparts can be also obtained by simply varying the feeding contents of Fe precursors. Experimental results indicate that incorporating Fe considerably adjusts Pt electronic structure and further lowers the binding strength of CO intermediates on Pt sites. Moreover, the strain, ligand and synergistic effect between Pt and Fe are much stronger in ordered PtFe catalyst than in the disordered one, endowing the ordered PtFe with an obvious higher activity, stability and anti-CO poisoning for methanol oxidation as compared to disordered PtFe as well as commercial Pt/C.