A method of adjusting brightness of a display panel includes a database creation step: storing attenuation data and a plurality of first brightness gain factors in a database. The attenuation data is performance attenuation data of a functional device of a display panel, and the first brightness gain factors are provided to display brightness of the display panel. A retrieving step: retrieving the attenuation data and the first brightness gain factors from the database. An adjustment step: adjusting the first brightness gain factors according to the attenuation data to obtain a plurality of second brightness gain factors.