An aperture measuring device and aperture measuring method for measuring the size of the aperture of a through-hole in a conductive structure is described to reduce the aperture measurement time and improve the working efficiency. The aperture measuring device includes: an aperture testing component for being inserted into the through-hole, wherein the aperture measuring device includes a plurality of resistor segments with different diameters, the individual resistor segments being successively connected in series in an order of the sizes of their diameters; and a measuring module for measuring the resistance value of a resistor segment unable to be inserted into the through-hole in the aperture testing component to determine the size of the aperture of the through-hole.