Circulating Fluidized Bed (CFB) boiler is the second largest number of boilers for power generation in Indonesia, after Pulverized Coal boiler. There are three main components in CFB boiler, namely: riser or furnace for performing circulating fluidized bed, cyclone for separating flue gas with solid particle and seal pot for returning solid particle from cyclone into furnace. During operation, CFB boiler frequently experience failure caused by overheating and abrasion. Common failure in seal pot is overheating caused by change in particle size distribution and flue gas flow rate.CFB boiler utilizes fluidization process in fuel combustion. The fluidization process uses materials in the form of sand particles (bed materials). The goal is for the temperature of the furnace to be distributed evenly. CFB boiler has one part called cyclone separator that serves to separate sand particles with fluid (flue gas). The research aims to determine the effect of bed particle size on the abrasion of cyclone CFB boiler PLTU Tenayan. The method is done using Computational Particle-Fluid Dynamics (CPFD) Software Barracuda Virtual Reactor 17.4. Geometry is created using SOLIDWORK 2020 and exported in*.stl format. The first particle variation uses the first particle size with SMD (Sauter Mean Diameter) of 57 μm, a minimum diameter of 2 μm, and a maximum diameter of 300 μm. The second particle variation uses a particle size with SMD 114 μm, a minimum diameter of 4 μm, and a maximum diameter of 600 μm. The simulation uses a variety of air mass flow by 80%, 100%, 110%, and 120% of normal air mass flow (69.43 kg/s). The drag model used is Wen Yu, and the Large Eddy Simulation turbulence model. The highest-pressure drop is on the standpipe. The particle speed is directly proportional to the speed of the fluid, which is due to the drag force of the particle. Particle volume fraction increases as air mass flow increases and particle size increases. The largest cyclone separator efficiency is produced by the second particle with an air mass flow of 83.3 kg/s of 96.44% while the smallest efficiency is produced by the first particle with an air mass flow of 55.5 kg/s of 85.05%. Efficiency will increase if the size and mass flow of air is increased. The most severe abrasion intensity lies in the cyclone barrel (cylinder) section. The larger the particle size, the greater the abrasion produced. The greater the mass flow of air flow, the greater the level of abrasion in cyclones.