Abstract: An ink supply system for printer to supply ink to a printer head includes an ink reservoir, a filter connected to an outlet end of the ink reservoir, a pump arranged at a front end of the filter, a pressure chamber connected to a front end of the pump, a valve arranged at a front end of the pressure chamber, a pressure sensor connected to the valve by a tube, and a controller for controlling the pump and the valve. The pressure sensor is arranged adjacent to the printer head to detect the ink pressure in the tube, and transmits a pressure signal to the controller. The pump can pump the ink forward to increase ink pressure or rearward to decrease ink pressure.