According to the urgent needs of active flexibility of equipment in a wide variety of industry sectors, such as precise assembly, removing, shaving, grinding, polishing and scrubbing on the surface of workpiece, an active constant pressure output device based on a cylinder was designed. According to design goals, it made a specific choice of the devices (including proportional pressure regulator, cylinder, guide rail, pressure sensor, etc.) which were used. And a weak signal conditioning circuit was designed for the pressure sensor, which can enhance the accuracy and anti-interference ability of the signal. And also, a data acquisition and processing board was designed to control the whole system and realized closed loop control of force output. And it received command of the host computer and uploaded the collected data through the RS485 communication. Finally, through a large number of dynamic and static pressure tests, it was shown that the output force error of the equipment is within ±3 N, the response time is less than 300 ms, the output force is greater than 200 N, and the performance meets the design goals. The development of this device opens up a new way for the design and research of active force control system.