The paper presents a fitness formula which is adopted to calculate the steel ball temperature uniform distribution time in the annealing process, analyses the steel ball temperature distribution in the process of heating. After the heat conduction equation of the steel ball is deduced, the spherical bessel function is adopted to solve it. The temperature distribution series solution is obtained. Using this formula, the steel ball temperature uniform distribution time of the different radius is calculated in the process of annealing. The result shows that the steel ball temperature uniform distribution time is the quadratic function of the steel ball radius. The time and radius data is adopted to deduce a second-order fitness polynomial. The steel ball temperature distribution is obtained in the different position. The steel ball temperature uniform distribution time is calculated by the fitness formula and the temperature distribution series one. The error between them is only 0.03%. The fitness formula can be used to calculate the steel ball temperature uniform distribution time. The change of the steel ball surface temperature is more severe than the internal. It often results in the crack of the steel ball in the annealing process.
