中文摘要：

本文介绍了MCNP程序中的几种重要性函数（几何重要性、正算权重窗、伴随权重窗）。几何重要性函数使用简便，广泛应用于各种模型；权重窗技术能大幅度提升计算效率，且适应性很好，基于虚拟网格的正算权重窗技术是复杂系统模型的首选重要性函数；伴随权重窗技术具有正算权重窗的优点，但需计算每个栅元的体积，不能处理含重复结构的问题。本文给出了两个数值算例，正算权重窗技术取得了最佳的效果。

英文摘要：

Several important functions （geometry important function, forward weight window, and adjoint weight window） of MCNP program were introduced in this paper. Geometry important function has some advantage of easy application, and it is widely used for nearly all models. Weight window can save substantial computer time when it is used judiciously. The mesh-based forward weight window can be used for almost all models. The adjoint weight window has almost the same advantage as forward weight window, but it is almost unavailable for complex geometry model because MCNP program can＇t calculate the volume of some cells （such as repeated structure cell or some asymmetrical cell）, which is indispensable for adjoint weight window generator. Two numerical examples were provided in this paper, and the computation efficiency of forward weight window is higher than that of the other two important functions.