Abstract: In order to explain the relationship among the powder feeding rate,scanning speed and the qualities of the clad coatings,the concepts of the specific energy input Er and the specific energy Eh formulated by L.C.Lim have been introduced with their experimental measuring methods which have been proved be successful.Based on metallographical measurement,the equations expressing the relationship between the specific energy input Er,the specific energy Eh and the parameters of the laser coated layer and the processing parameters has been derived.The factors effecting the specific energy input Er and the specific energy Eh have been studied carefully.When the powder feeding rate vf and scanning speed vs increase,the specific energy Er and the specific energy Eh decrease under definite laser power P and beam spot dimension.A reasonable explanation why a minimum is observed in the relationship between the scanning speed and the specific energy Er is presented.In the meantime,it is the theoretical foundation for further study the microstructure,mechanism of solidification and processing parameters.