The invention relates to an automatic measuring device and a measuring method of elementary charge and electric quantity. The automatic measuring device comprises an aluminum alloy case, an oil drop box, a power switch with an indicator, a three-way switch, a voltage regulation knob, a timing button, a image data transmission line, a digital microscopy camera, a liquid crystal display, and a microcontroller circuit board. The microcontroller circuit board comprises a digital-to-analogue conversion circuit, a counter electrode drive circuit, a crystal oscillator circuit, an image processing circuit and a microcontroller. The automatic measuring device and the measuring method of the elementary charge and electric quantity achieve precise regulation of voltage between plate electrodes, overcome the defect that oil drops and stains are difficult to distinguish by a traditional device due to the fact that resolution ratios are low and definition is poor, and is capable of accurately measuring speed of uniform declination of the oil drops and automatically computing electric quantity of elementary charge and measurement errors.