This paper studied the deposit process of electroless Ni-P on die casting magnesium alloys using SEM and GDA spectrum analysis instrument etc. The results indicated that pre-treatment made magnesium alloys surface netted-porous, loose MgF2 and AIF3 layer formed after activation process. The initial deposit process of electroless Ni-P was precipitation of Ni without P atom, followed by Ni nucleating and growing up, the Ni of self-catalysis formed, the nickel phosphorus began to co-deposit. There exited mixing layer composed of complex compound, fluoride, plating liquid and Ni in the initial deposit coating.