Abstract: Gelation Process is the main approach to prepare the UO₂ ceramic microspheres,whichserves as the core of the high temperature gas cooled reactor（HTR） fuel elements.In the process of preparing the microspheres,the casting solution is first emitted from the nozzle into an air section in order to obtain droplets with specific degree of sphericity.The droplets are subsequently injected into the gelation section and solidified.The distance from the nozzle to the ammonia section is the length of the air section.To prepare the UO₂ ceramic microspheres with higher sphericity,a mathematical model was established to calculate the optimized length of the air section theoretically and the calculated outcome has been validated by experiment.