Abstract: This paper have designed the whole structure of round baler with prepressing device. The whole baler was composed of drive system，pickup， feeder， bale chamber， twine and tying mechanism， hydraulic system， autocontrol system，bale discharger，and so on. At the same time，analyzed the characteristic of bale chamber，designed the whole structure drive system，described the gyropilot process of the baler， expatiated the function of pickup， feeder，rollers， twine and tying mechanism.