Chemical composition differences between the feedstock powder and the final coating of a series of composite abradable coatings were investigated. Graphite filler material mass distributions in the coating, overspray powder and burned power is calculated. A preliminary mechanism of graphite loss during the deposition process is established. It is found that the graphite content in the coating is significantly lower than that in the feedstock powder. Over 70% graphite in the feedstock powder is lost during the deposition process. Melting and shrinkage of the nickel shell of the nickel cladded graphite particle as flying through the flame, which resulted in the exposure of the graphite core to the flame and substrate, is the main reason for graphite loss and chemical composition change between the feedstock powder and the final coating. A random manner of particle structure transformation in the flame and its reactions with the spray environment is concluded as an important reason for the poor process repeatability of abradable coatings.