The present invention discloses a backlight adjustment method and system, a backlight module and a display device. The backlight adjustment method includes: calculating a first outgoing light brightness of an backlight block corresponding to each image block; dividing a backlight source into a number of closed areas according to the first outgoing light brightnesses of the backlight blocks; calculating the number of backlight blocks included in each of the light-emitting closed areas; looking up a corresponding drive current in a preset correspondence table, wherein predetermined correspondence between the number of backlight blocks and the drive current applied to light up the corresponding number of backlight blocks and make an actual brightness of the corresponding area equal to a preset brightness is recorded in the correspondence table; and outputting the drive current obtained by the lookup operation to the backlight blocks in the light-emitting closed area.