采用BEAMnrc程序构建医用直线加速器治疗头模型，模拟计算几种单一材料或复合材料构成的均整器对应的射野剂量分布情况.通过对各组射野离轴比(offaxial ratio，OAR)、离轴剂量分布和能量注量分布曲线进行分析并与GB 15213—94国家标准对照，设计具有较好均整度的复合材料均整器.讨论粒子角分布、X射线剂量利用率以及带电粒子污染问题，说明所设计的均整器具有射野内剂量分布平坦、粒子前向性好和带电粒子污染小等优点.

Using BEAMnrc to model the beam geometry of medical linear accelerator treatment head, X-ray dose distribution for a field sized 10 cm×10 cm is calculated after the X-ray passed through a flattening filter consisting of single material or multimaterial. By comparing the results of the off-axial ratio (OAR), the offaxis dose distribution and off-axis energy fluence distribution curves under GB 15213—94, a multi-material flattening filter with better flatness is designed. Angular distribution of particles, X-ray dose rate and charged particles pollution are discussed. The results show that this flattening filter has advantages including good flatness, satisfactory forward shooting property of particles, and low pollution of charged particles.