King grass is a perennial hybrid pennisetum with cluster rooting and high stem. It has good feeding value, but it is difficult to harvest mechanization. Aiming at the problems of poor agronomic matching and insufficient supporting power in the operation of the existing king grass harvester, a self-propelled tracked chassis of the king grass harvester was designed. According to the work requirements of reducing stubble rolling and speed stable harvesting, the walking and stepless variable speed driving device were designed. The hydraulic power steering system and frame were designed and selected based on the terrain features of small plots and gentle slopes. The stability performance was analyzed, and the whole machine was tested. The results showed that the maximum driving speed of the chassis was 9.02km/h. Its minimum turning radius was 1349mm, and the maximum climb was 26°. The whole machine had no side slip and tipping phenomenon when driving on the contour line of the lateral slope of 15°~16°. The time of reliable parking along the uphill and downhill directions on the longitudinal slope of 10°~12° was more than 5min. When harvesting in the field with a slope of 8°~9°, the whole machine can achieve a stepless speed change of 0~4.19km/h, which had sufficient power, and ran smoothly. And the average stubble rolling rate of king grass was 7.43 %. The research result showed that the designed chassis can meet the mechanized harvesting requirements of king grass planting on small plots and gentle slopes.