The invention relates to a preparation method for a controllable duplex metal alloy nano particle. The metal alloy nano particles is a Pt/Pd-M alloy nano particle, wherein the M is selected from Ni, Fe, Co, Mn, Pd, Zn, Cu and Mo; during preparation, n-butyllithium is used as a strong reducing agent and oleylamine and tri-n-octylphosphine are used as protective agents to reduce acetylacetone, chlorate or acetate of the Pt/Pd-M (M= Ni, Fe, Co, Mn, Pd, Zn, Cu,Mo) at the same time so as to form the uniform and size-controllable Pt/Pd-M alloy nano particle without a concentration gradient. The preparation method is simple and controllable in preparation technology, and can solve the problem that when precursor reduction potentials of two metals are greatly different, one metal can be reduced in prior, so that the alloy nano particle can not be obtained easily, provides a better and universal synthetic method for the preparation of the duplex metal alloy nano particle, and provides a key precursor for the preparation of a new generation of metal-oxide nano hybridization body catalyst used for selective hydrogenation reaction.