The reutilization of waste plastics as a fuel in the cement kiln precalciner process was investigated. For uniform feeding into the fluidized bed calciner, waste plastics were prepared to form of pellet type by shredding, melting, pressing, cutting and screening. We examine the property of combustion for different pellet size using the Computational Fluid Dynamic analysis program to minimize a risk and to optimize condition of an actual proof plant. Based on the results from the computational fluid dynamic analysis, the waste plastic for the industrial scale experiment were used as 20mm, 50mm and 100mm in size. The experimental result of an actual proof plant showed comparatively good correlation with the computational fluid dynamic analysis.