Ni-P alloy coating on Titanium alloy was obtained by electroless plating method. The influence of annealing temperature on the adhesion of the Ni-P coating was investigated .Dynamic equation to describe the interface layers thickness, diffusion heat treatment temperature and holding time were established by SEM analysis. The product of the diffusion interface and the influence of different annealing temperature on the coating of thermal stress were studied by X-ray diffraction. The results showed that the Ni-P coatings were no diffusion layers when treated at 400℃ for 2 and 4 hours, and diffusion layers appeared when treated above 400℃. The dynamic equation, , can be obtained according to the relations of the thickness of the diffusion layer and the time and temperature of heat treatment. The thermal stress of coating increased significantly after heat treatment; the adhesion of the coating with heat treatment was much higher than that of without heat treatment. The best adhesion of the coating can be obtained when the heat treatments were at 400℃2h、400℃4h、500℃4h.