有关接触电势差的描述,一般《电磁学》书籍只进行了定性的讨论,很少给出定量的分析。为此,本文将从经典电子论出发,作一番推导。根据经典电子论,产生接触电势差的原因有二:①两种金属的逸出功不同;②两种金属的自由电子数密度不同。现分别论述如下: The description of the contact potential difference, the general “Electromagnetism” books were only qualitative discussion, the quantitative analysis is seldom given. To this end, this article will proceed from the classical electronic theory, for some deduction. According to the classical theory of electrons, there are two reasons for the difference in contact potential: ① The work functions of the two metals are different; ② The numbers of free electrons in the two metals are different. Now are discussed as follows: