A method and device for adjusting a display parameter, and a display device. An ambient brightness level is used as a criterion to adjust a brightness level of an intermediate gray level of a displayed image, such that a corresponding display parameter can be adjusted to be closer to the criterion within an appropriate allowable floating range, thereby providing a displayed image that is safe and comfortable for the eyes. The method comprises: detecting an ambient brightness level (101); determining an adjustment parameter of a display device corresponding to a preset condition, the preset condition comprising a difference between a brightness level of an intermediate gray level of the display device and the ambient brightness level being less than or equal to a preset brightness value (102); and adjusting, according to the adjustment parameter, brightness levels of at least a portion of gray levels of the display device (103).