Abstract: On the basis of the analysis of the feeding pattern of the coating material,its behavior in the laser beam and the attenuation of laser beam by particle cloud during the process of laser coating with automatic powder feeding,the methods to calculate the interaction efficiency η of laser and particle speed v0 are presented.The equation of the interaction efficiency η is established and expressions relating the parameters in the processes are obtained.The factors affecting the interaction efficiency η is studied carefully.The interaction efficiency η is calculated by means of metallography.A reasonable explanation about why a maximum interaction efficiency η is observed with the scanning speed varies is presented.