本文描述用矢量势计算H-120回旋加速器主磁铁磁场的有限单元法,由小增量牛顿拉斐逊迭代法解算最终得到的非线性方程组,每步采用LDL~T分解法。比较了场分布的计算值与实测值,偏差小于1％。 This paper describes a finite element method for calculating the magnetic field of the main magnet of a H-120 cyclotron using a vectorial potential. The resulting system of nonlinear equations is solved by a small incremental Newton-Raphson iteration method, using LDL-T decomposition for each step. The calculated and measured field distributions are compared with less than 1% deviation.