Abstract: The one-dimensional Fokker-Planck equation was solved by finite volume method. The reliability of program was verified by simulation of electron self-collision. The results show that the numerical scheme assures positive distribution function and particle number conservation. It is an effective method of solution for Fokker-Planck equation. And the overshoot of the Maxwell distribution that arouse from Fokker-Planck equation solving by traditional numerical method was eliminated. Furthermore, the evolutions of ion distribution function and temperature were simulated in neutral beam injection heating on the HL-2A. The results show that the ion distribution function tends to non-Maxwell distribution as the neutral beam injects, and the ion temperature rises rapidly and then reaches stability. The effects of beam power and energy on the ion temperature were investigated, and the results show that the ion temperature increases with the beam power and energy. The change is more obvious by increasing beam energy than power.