Abstract: Nanometer Ni－Co alloy coating is prepared by pulse electrodeposition in external static magnetic field.The external static magnetic field is vertical to the electric field orientation.The result by using the scanning electron microscope and X－ray diffractrometry shows that static magnetic field is introduced to refine the crystal grain size of the plating,making the nanometer Ni－Co alloy coating becomes smooth and compact.When the applied voltage is 7V with static magnetic field,the hardness of coating will reach the maximum value 583HV.The hardness of coating with the static magnetic field was raised by 112HV as that without the magnetic field applied.The service life of the diamond tool of 7V static magnetic field is 1.21times as that of the tools without magnetic field applied.