An adjustable desk lamp includes at least two buttons, a lamp panel, a stand, and a support arm assembly. The stand includes at least two button housings. Each of the button housings is filled with liquid and receives one of the buttons. The arm assembly is attached to the stand. The arm assembly includes at least two channels and at least two support posts. Each of the channels communicates with one of the button housings and is filled with liquid. One end of each of the posts is received in one of the channels, and another end support the lamp pane. When one of the buttons is operated, the liquid in the button hole receiving the operated button and the channel communicating with the button hole is displaced, and the post received in the channel moves downwardly or upwardly, thus the lamp panel can cast light at a different angle.