Pre-treatment process is the key step for electroless plating.Once a suitable pre-treatment film is in place,the desired metals can be plated.In this paper,Ni-P coating was successfully prepared on AZ33 magnesium alloy with Mg(OH)_2 pre-treatment film by electroless plating.To investigate the role of MgF_2in Ni-P coating,the deposition procedures between Mg(OH)_2 pre-treatment film and Mg(OH)_2-MgF_2pre-treatment film(a traditional process) were compared.The surface morphology variations of coatings were observed with scanning electron microscopy and the compositions were analyzed by energy dispersive spectrometry.The results showed that during the plating,both MgF_2 and Ni-P deposited at the initial stage,and MgF_2 distributed in the bottom of the coating,forming a transitional interlayer with NiP.According to the heat quench test,a poor adhesion of the coating mainly occurred between the MgF_2and Ni-P coating. Pre-treatment process is the key step for electroless plating. Once a suitable pre-treatment film is in place, the desired metals can be plated.In this paper, Ni-P coating was successfully prepared on AZ33 magnesium alloy with Mg (OH) _2 pre-treatment film by electroless plating.To investigate the role of MgF_2in Ni-P coating, the deposition procedures between Mg (OH) _2 pre-treatment film and Mg (OH) _2-MgF_2pre-treatment film (a traditional process) were compared. The surface morphology variations of coatings were observed with electron microscopy and the compositions were analyzed by energy dispersive spectrometry. The results showed that during the plating, both MgF_2 and Ni-P deposited at the initial stage, and MgF_2 distributed in the bottom. of the coating, forming a transitional interlayer with NiP. Accredited to the heat quench test, a poor adhesion of the coating mainly occurred between the MgF_2 and Ni-P coating.