提出了金属薄膜厚度对薄膜中自由电子的平均自由程影响的物理模型,并给出了薄膜中自由电子的平均自由程的修正公式.理论研究表明：当膜厚小于自由电子的平均自由程时，薄膜中电子平均自由程随膜厚的减小而减小;当膜厚大于或等于自由电子的平均自由程时，薄膜中电子的平均自由程与块状材料一样.利用薄膜中电子平均自由程的计算公式，修正了薄膜导电率的基本理论表达式，再利用金属薄膜的反射率与薄膜导电率的关系，得出金属薄膜厚度对其光反射率的影响.计算机模拟表明：当薄膜厚度小于电子自由程时，金属薄膜反射率随薄膜厚度变化而呈非线性关系.

A physical model was proposed to illustrate the influence of metal film thickness on electrical mean free path, and the formula of electrical mean free path was modified based on this model. The results demonstrate that the electrical mean free path decreases with film thickness decreasing, when the film thickness is less than the mean free path. Otherwise it is a constant as bulk material. The film conductivity expression was also modified based on this formula. Combining with the relationship between metal films′ conductivity and reflectivity, the formula of thin film conductivity with different thickness was put forward. Computer simulations show that when the film thickness is less than the electrical mean free path, the changes of metal film reflectivity are nonlinear.