A method and a circuit for modulating an eye diagram amplitude, a method and a circuitry for data transmission, and a display device are provided. The method for modulating an eye diagram amplitude includes: an eye diagram amplitude setting step, including: setting, by a base eye diagram amplitude setting unit, a base eye diagram amplitude for a source driver; a preset differential signal outputting step, including: outputting, by a preset differential signal outputting unit, a preset differential signal to the source driver; a comparing step, including: comparing, by a comparing unit, a differential signal received by the source driver and the preset differential signal to obtain a comparison result; and a modulating step, including: modulating, by an eye diagram amplitude modulating unit, an eye diagram amplitude of the source driver based on the comparison result.