A simulation model of a wheeled tractor was built using the multi-body dynamics software RecurDyn. The model consisted of four wheels, front and rear axles, and a body frame. An interaction model between tires and soft soil was established using the Soil-tire module of RecurDyn. The simulations of displacement and force of the tires were conducted on 20° up-slope, 44° ultimate up-slope, 20° down-slope and 34° ultimate down-slope roads respectively. The performance of a wheeled tractor over a cylindrical obstacle was analyzed under two different speeds. Results showed that forces of the front wheel were different on different slope roads. The maximum impact force of the front wheel increased by 68% as the up-slope increasing from 20° to 44°. The maximum impact force of the front wheel decreased by 8% when the down-slope changing from 20° to 34°. The maximum force of the front wheel decreased by 16% when the wheeled tractor over a cylindrical obstacle with the speeds decreasing from 1.356m/s to 0.678m/s.