Abstract: Abstract: Silaging nutrient-rich phase grass with bags in the field can reduce nutrient loss, maintain green feed nutrients, and facilitate long-term preservation; thus promotes the growth of good livestock. To facilitate direct storage of forage harvested in the field, one self-propelled grass silage combined bagging machine was developed.. It integrated the cutting device, a conveyor feeding device, a crushing and throwing device, vertical auger conveyor equipment, grass bagging density control device. And their key device parameters were calculated. The self-propelled grass silage combined bagging machine used disc cutter to cut grass, the blade root diameter and top diameter were 500 and 620 mm, and the critical forward speed of the machine was 17.9 km/h so that leakage could be prevented and repeat cutting could be reduced. The designed grinding hob diameter and the width were 550 and 480 mm. it's rated rotating speed was 1600 r/min and the linear velocity of the feed roller was from 2.1-17.1 m/s when the length of the cutting grass was 5-40 mm. The diameters of the front and intermediate feed roller were 300 and 260 mm, and the calculated rear feeding roller diameter was 90 mm. In order to minimize forage accumulation, the designed throwing roller diameter was 300 mm, the width was 510 mm, the angular velocity was 2 600 r/min, the leaf number was 4, and the angle of thrown pieces of angle was 20°. The displacement and velocity equations at any moment from the start. Grass compressed by screw auger before output from the silo. The compression ratio of the screw mechanism can be adjusted for achieving the desired output squeeze effect. The three different of compression ratio screw auger were designed for different types of forage, and spirals can be changed by the exchange of connecting flange. According to squeeze theory, the designed spiral inner diameter was 100 mm and screw conveyor segment pitch was 345 mm at the beginning of variable pitch segments, meanwhile the surface of screw extruder was polished and longitudinal grooves in the barrel were built for increasing the extrusion effect. The crushed forage was loose and easy to squeeze, and had a large volume gradient. Then the volume gradient became small, and pitch gradually becomes small, so rational compression ratio made compression effect better. Finally, the critical rotation speed was calculated and was 99 r/min. In the self-propelled silage harvester, this innovative design combined automatic pneumatic tying device could greatly reduce labor intensity. Working performance test of the developed prototype was conducted with forage whose moisture content is 78%. Results showed a stubble height was 5-15 mm, cutting leakage loss was 0.85%, average bagging density was 320 kg/m3, average bagging time was 30 s per bag, tying rate was 100%.With average forward speed at 2.3 m/s, operation capability of the machine can achieve 0.53-0.67 hm2/h without clogging. The presented study provides a new approach for the harvest and storage of silage grass.