Abstract: This paper observes and analyses the structural transformation of electroless Ni-Co-P coating heat-treated under different temperatures with H-800 transmission electron microscope. The results show that the amonphous-crystalline transition of the coating will take place when the heat treatment temperature exceeds 350℃.Compared with the crystallization process of Ni-P coating, it can be concluded that the presence of the third element of cobalt improves the heat stability and raises the crystallization temperature of electroless coating.