Abstract: Fully ceramic microencapsulated (FCM) fuel which is a kind of cylinder fuel and fabricated by dispersing TRISO particles into SiC matrix has been used as gas-cooled micro reactor fuel and accident tolerant fuel. The distribution of TRISO particles in FCM pellets will affect the performance of the fuel in the reactor. The FCM fuel pellets were fabricated by spark plasma sintering (SPS) with the green body which was the mixture of over coated TRISO particles and SiC power containing sintering aids. Four FCM fuel pellets were extracted from four different real fabrication lots by random means. Neutron photography test and computed tomography method were used to study the distribution of particles in the four real pellets. Grayscale images in 360° around the pellet were taken, and through the image denoising algorithms and algebraic reconstruction technique, the center coordinates of all particles in the four pellets were obtained. The real distribution of particles in different directions was investigated by studying the volume fraction of particles in the pellets through axial and radial direction with the coordinates. The 3D models of the real distributed pellets and the assumed pellets with regular distribution of particles were established with the assumption that all particles are in a uniform shape. On the basis of the conservative operating condition for gas-cooled micro reactor, the performance of real distributed pellets and assumed pellets during the normal operation of the reactor was calculated through finite element code. The distribution analysis results show that in axial direction particles are nearly well-distributed but in radial direction particles trend to gather towards the center at the outer part of the pellet and are nearly well-distributed at the center of the pellets. The performance analysis results show that temperature and temperature gradient of the real pellets in the reactor are higher than those of the assumed regular distributed pellets with the same particle’s volume fraction but lower than that with higher particle’s volume fraction. The particle distribution through axial direction at the center of the pellet is intensive and stable which means that particles gather together in the center and become nearly saturated. Consequently, the over coating thickness of the particles during fabrication will be improved to reduce the cluster of particles in the future. Since the increased range of the temperature and temperature gradient is limited and lower than regular distribution pellets with 45% volume fraction of particle, the safety of the reactor won’t be affected by the inhomogeneous distribution of particles in the real pellets.