Abstract: A negative-pressure control device for an ink-supply system comprises a box, an ink-jet head, an adapter and a set of releasable check valve mutually communicated. The box has thereon a water outlet, and is provided therein with a liquid level gauge to control and maintain a constant level of the ink in the box; by operation of a releasable check valve set, air in the ink-jet head and the adapter presents the state of negative-pressure, this maintains a balance state preventing the ink from dropping when the ink in the ink-jet head and the water outlet is subjected to attraction of the air with the negative-pressure; when the ink-jet head jet prints downwards, it can automatically supplement ink to get an effect of continuous jet printing; the control device is suitable for a jet-drawing machine to place an advertising board with a propaganda paint or a poster etc. for printing.