The present invention directs to a method for automatically compensating a common electrode voltage, comprising: calculating an average shift amount of a common electrode voltage according to gray scale data in a line on a displayed image, processing the average shift amount of the common electrode voltage to be a digital signal then converting it into an analog signal then into an average shift amount voltage waveform, and superposing it with a common electrode voltage waveform to form a new output signal waveform for driving the common electrode; the present invention also directs to a device for automatically compensating a common electrode voltage, comprising a data input module, a looking up module, a data operation module, a data encoding and converting module, a waveform generator and an operational amplification module. In the method and device for automatically compensating the common electrode voltage according to the present invention, a common electrode is driven at same time when a pixel electrode in one line on a liquid crystal display screen is driven, charges on the common electrode are compensated, such that common electrode voltage delay is avoided and image quality displayed by the liquid crystal display screen is improved dramatically.