史密斯图（Smith chart）是一款用于电机与电子工程学的图表，主要用于传输线的阻抗匹配上。一条传输线（transmission line）的阻抗（impedance）会随其物理长度而改变，要设计一套阻抗匹配（Impedance matching）的电路，需要通过不少繁复的计算进程，史密斯图的特点便是省却一些计算进程。

该图表是由菲利普·史密斯（Phillip Smith）于1939年发明的，当时他在美国无线电公司（RCA）工作，曾说过，「在我能够使用计算尺的时候，我对以图表方式来表达数学上的关联很有兴趣」。但日本无线电信公司的水桥东作在1937年所发表的论文中就已提出这种图表，比菲利普·史密斯早2年。因此在日本有主张此图应改名为「水桥图」或「水桥-史密斯图」。

The Smith chart, invented by Phillip H. Smith (1905–1987), is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. Use of the Smith chart utility has grown steadily over the years and it is still widely used today, not only as a problem solving aid, but as a graphical demonstrator of how many RF parameters behave at one or more frequencies, an alternative to using tabular information. The Smith chart can be used to simultaneously display multiple parameters including impedances, admittances, reflection coefficients, scattering parameters, noise figure circles, constant gain contours and regions for unconditional stability, including mechanical vibrations analysis. The Smith chart is most frequently used at or within the unity radius region. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis.