The present invention discloses a feed system with a constant pressure. The feed system comprises a feed container which has a depressurize port mounted on its top, a intake port mounted at its side, and a feed port mounted on its bottom, contains a liquid material being a medicine or a liquid glue mixture; a intake structure which comprises a throttle pipeline and a throttle valve; a opening controller which connects to the throttle valve and the pressure sensor, for controlling the intake structure. The advantage of the feed system is to control the feed flow rate so as to maintain a constant during the feed process, particularly in the hybrid feed system. By steadily controlling the output flow rate, the mixed proportion is controlled to generate the product with the stable quality when two or more liquid materials must be mixed according to the specific proportion.