The mechanical work such as weeding, spraying and fertilization requires the chassis should move along the crops’ row spacing. Since the row spacing of different crops is various and the row spacing of the same crop in different regions or by different planted methods are also not uniform, there are some problems such as poor flexibility, difficult passing ability, and tendency to destroy the crops when the existing agricultural vehicles running. So the agricultural chassis’ wheel track should be adjustable basing on the different crop spacings, during which the steering must be difficult. At present, steering has been solved by hydraulic drive, servo control the turning wheel, or servo motor control the turning wheel, which are more complicated. According to the demand for the chassis’ adjustable wheel track varying with different row spacings, the linkage principle of wheel track and steering was researched. Based on the Ackerman steering and parallelogram mechanism，the steering mechanism with adjustable wheel track was proposed in which the wheel track adjustment and steering can be completed independently and simultaneously, and the calculation method of key parameters and steering error were ascertained. A kind of agricultural chassis with adjustable wheel track was designed which included steering mechanism with adjustable wheel track on front bridge, adjustable wheel track mechanism and driving system on rear bridge. Basing on the characteristic of mechanism movement and the criterion of mechanical design, considering the present related chassis and the crop planting mode of China, the key parameters of the chassis has been determined. And the key parameters of steering mechanism with adjustable wheel track on front bridge were determined and optimized by taking minimum wheel track as basic wheel track. The steering error calculation results in different wheel tracks showed that the chassis’adjustable wheel track and steering performance could meet the agricultural needs.