On the basis of an analysis on the feeding pattern of the coating material and its behavior in the laser beam during the process of laser coating with automatic powder feeding, a heat equilibrium equation was established and expressions relating the parameters in the process were obtained. The parameters include the grain size of the coating material, its distance of motion in the beam, heating temperature and power density. It is pointed out that the necessary condition for obtaining optimum coating in the process with automatic powder feeding is that from the instant of the powder grains entering the laser beam to the instant that the grains reach the substrate surface, the powder grains must be persistently within the laser beam to fulfill the above condition. The laser beam must have enough width along the scanning direction, and this width can be calculated by the expression suggested in this paper. Finally, the principle for matching the process parameters to obtain an optimum coating is presented.