The invention relates to a screw clamping device used for assisting a screw tool in positioning screws. The screw tool provides rotary power to be outputted to the screws. The screw clamping device comprises a body, a clamping mechanism and a driving mechanism. The body is connected with the screw tool. The clamping mechanism is located at the longitudinal front end of the body along an axis of the body, can move between the clamping position for clamping the screws and the loosening position for loosening the screws, and comprises at least two clamping arms. The driving mechanism drives the clamping mechanism to move and comprises at least two groups of connecting units correspondingly connected with the clamping arms and guide units correspondingly guiding the connecting units to move, and each group of connecting units comprises a first connecting piece and a second connecting piece. The first connecting pieces move longitudinally and horizontally, the second connecting pieces at least move longitudinally, and accordingly the clamping arms are driven to generate pivotal movement and longitudinal linear movement.