A pneumatic ink-jet system is applied in an inkjet printer and uses a negative pressure generator, which is designed according to the Bernoulli's Theory, with a stable airflow in a certain speed to generated stable pressure inside at least one inkpot and at least one print head. Therefore, the at least one print head is kept in an appropriate wet state and the quality of printing is enhanced. Moreover, a top surface of the ink inside the at least one inkpot can be controlled to be higher than the at least one print head, so the pneumatic ink-jet system can be applied in a large format inkjet printer.