Abstract: Aiming at problems of poor adaptability of tractors in hilly and mountainous areas, large turning radius in field, easy to damage crops, long time-consuming and low efficiency, a 504-type hilly tractor chassis that could turn in situ was designed．Whole machine adopted a four-wheel drive walking system, with forward and backward speeds of 0-5 km/h and stepless speed regulation．Transmission system adopted mechanical "H" transmission route, and driving forces on the left and right sides were separated independently through design of inner and outer double shafts of longitudinal beam．Clutch type steering transfer gear was used to complete control of different working states of chassis through combination of two tooth type clutches in steering transfer box．The two-way power realized the forward, reverse, left and right radius steering and in-situ steering of tractor through combination of four states: forward rotation + forward rotation, reverse rotation + reverse rotation, forward rotation + reverse rotation, reverse rotation + forward rotation．Results showed that the maximum traction force of whole machine was 10.78 kN, the maximum and minimum total transmission ratios were 732.50 and 73.25, respectively．The maximum and minimum speeds of front and rear drive axle drive shafts were 31.07 and 6.21 r/min, respectively．Ratio of wheelbase to wheelbase of chassis was equal to 1, and sum of sliding resistance moment and rolling resistance moment of chassis was less than driving moment of chassis, which could realize in-situ steering in narrow ground, reduce empty travel of tractor in field operation, improve operation efficiency and effectively protect crops．