In order to express the relationship between the dilution and the processing parameters, The concept of dilution is formulated. The equation expressing the relationship between the dilution and the parameters of the laser coated layer and the processing parameters was derived based on metallographical measurement. The experimental method for determining the dilution in laser coating process by powder feeding method was designed. By varying the powder feeding rate Vf and scanning speeding Vs under definite laser power P and beam spot dimensions, coatings with different thickness were obtained. The dilution was calculated with the help of metallographical measurement. The factors which affected the dilution were studied carefully. When the powder feeding rate and scanning speeding Vs increase, the dilution become smaller. A reasonable explanation on why a minimum value is observed in the relationship between the scanning speeding and the dilution is presented. In the meantime, it is the theoretical foundation for further investigation on the relationship between the microstructure,mechanism of solidification and the processing parameters.