A semi-auto sliding mechanism is provided, including a first member, a second member, a first rack, a second rack, a pinion gear pivotally connected to the second member, and a clockwork spring connecting the pinion gear to the second member. The first and second racks are disposed on the first member. When the first member is moved relative to the second member to a first position by an external force, the pinion gear rolls along the first rack, and an elastic potential energy is stored in the clockwork spring. When the external force is released, the clockwork spring impels the pinion gear to rotate along the second rack, such that the first member moves relative to the second member from the first position to a second position.