A new counter-current type of moving bed reactor was devised for AlN coatings of Si3N4 fine particles in the form of agglomerates by chemical vapor deposition. The influence of process parameters, such as reaction time and temperature, input concentration of gas precursor, and the agglomerate size, was investigated in relation to total quantity of deposited AlN inside the agglomerates. A simplified reactor model was used to analyze the deposition data. As a result, the conversion of Si3N4 particles to their composite with AlN increased with increasing temperature and concentration of AlCl3 reaction gas and with decreasing agglomerate size. Thus, it has become possible to produce a sort of surface modified ultra-fine particle at certain coating ratios continuously.