The invention discloses a pneumatic system of a press machine. The following main technical scheme is adopted: an air storage barrel is divided into an upper part and a lower part by a partition; great air pressure fluctuation easily caused by a jacking cylinder during a working process is limited from being serially connected to the upper space by a check valve; a pressure sensor is installed on an air pressure channel of a brake; and a brake air pressure of the brake can be monitored through sensing so as to be always in a normal state, thus the brake reliability is ensured.