A point-of-sale (POS) system with a display viewing angle adjustment device includes an adjustment device securely mounted on a rear cover of a display and pivotally connected with a support arm of a base. The adjustment device includes a support plate and a fixing plate securely mounted on the rear cover of the display. The support plate has two side legs, and the fixing plate has two slide slots for the side legs of the support plate to slidably mount through the slide slots, such that the support plate can be moved up and down and is mounted between the screen and the fixing plate. The side legs of the support plate are pivotally connected with the support arm of the base. Because of the support of the support plate and the slide slots of the fixing plate, the screen can be moved up and down to conveniently adjust a display viewing angle.