Abstract: Aiming at problems of difficult field head steering and easy compaction of working block of hilly and mountain tractor, an adaptive chassis of hilly tractor was designed．The engine was horizontally arranged on the frame．The power was transmitted from one end of engine through belt to transmission parts for chassis driving, and the other end was output for field harvesting and other operations．The steering system was designed with broken trapezoidal structure and adopted two steering modes: front wheel deflection and four-wheel deflection, which could realize all-hydraulic four-wheel out of phase steering．Results showed that the maximum and minimum driving speed of chassis were 10.98 and 0.91 km/h, respectively．The maximum and minimum transmission ratio of the chassis were 370.37 and 61.38, respectively．The minimum turning radius of front wheel deflection of the chassis was 2003 mm and the minimum turning radius of four-wheel deflection was 1494 mm．The hilly mountain tractor has good adaptability to small plot operation．