The invention discloses a fuel pellet and a preparation method thereof. The fuel pellet comprises a first fissible part and a second fissible part filling the inner side of the first fissible part, wherein raw materials of the second fissible part comprise a fissible material and additives, and a high-thermal-conductivity area is formed by the second fissible part. Under the condition that life cycle of nuclear fuel is not influenced obviously, the high-thermal-conductivity area is formed by the second fissible part by the aid of the additives, and the center temperature of the pellet can be reduced under the condition of the same heating power; the loading quantity of the fissible material in the pellet area can be properly reduced in the presence of the additives, then the fission density is reduced, the center temperature of the pellet can be reduced finally, and the thermal margin of a reactor is increased. The second fissible part is arranged in the first fissible part, so that the whole fuel pellet is enabled to be in a solid structure, the strength of the fuel pellet is higher than that of a fuel pellet with a hollow structure, and the pellet is prevented from cracking after bearing high stress; an inner passage with smaller MDNBR (minimum departure from nucleate boiling ratio) does not exist, and DNB is avoided more easily.