双对数坐标系是数学或其他自然科学中的用语，是二维笛卡尔坐标系的一种特殊形式：其使用的是对数刻度，即其两条坐标轴的刻度间长度并不与刻度成比例，而是与刻度的对数成比例。

由于其两条坐标轴都是非线性刻度，函数在这种坐标系下将呈现出一条直线，其中b是斜率，a就是y坐标轴上 x = 1的点。这种图像的用途之一是，如果一些数据符合上面的函数，但是参数a，b未知，则可以通过将点绘制在这种图像上的方法来得到。

In science and engineering, a log–log graph or log–log plot is a two-dimensional graph of numerical data that uses logarithmic scales on both the horizontal and vertical axes. Monomials – relationships of the form – appear as straight lines in a log–log graph, with the power and constant term corresponding to slope and inte****t of the line, and thus these graphs are very useful for recognizing these relationships and estimating parameters. Any base can be used for the logarithm, though most common are 10, e, and 2.