Fe-based amorphous coatings have many excellent performances, such as good corrosion resistance, high hardness, satisfactory magnetism, etc. In this paper, Fe-P amorphous coatings were prepared by electrodeposition method, and the phase transformation, microstructure, and hardness of the coatings heated at different heat-treatment temperature were investigated. The results show that Fe-P amorphous coatings begin to crystallize when heated at 300°C, the α-Fe(P) solid solution appears when heated at 330°C, and FexP(X=1,2,3) compounds separate out from the solid solution when heat-treatment temperature is up to 370°C. During the process of heat-treatment, hardness of the Fe-P coating increases as the reinforcement result of solid solution and dispersed phase in the coatings, and the hardness reaches the maximum 1100 HV at 370°C. When heat-treatment temperature is higher than 460°C, dispersed phase in the coatings will grow up, which is called Ostwald Coarsening Phenomenon, and hardness of the coating decreases quickly.