Along with the dramatically growing use of agricultural tractors, the associated vehicle lateral stability has been found to greatly affect operation efficiency and human safety. According to characteristics of the low speed driving condition of tractor on slope ground, a scaled experimental system for measuring the tire-ground reaction force was built. By applying the 3D printing technology, a scale-model-tractor attached with implement and the random terrain surfaces for the tractor to pass over was developed. Taking the uphill wheel load of the tractor as the main reference parameter, the lateral stability evaluation indexes for tractor’s front and rear wheels were proposed. The choice of tire type, ballast weight, front and rear track widths, and implement height were selected as the control factors, while introducing the terrain roughness in classes E and F as the noise factors. Employing the Taguchi design of experiment, factorial significances were investigated by the corresponding ANOVA analysis. The experimental results showed that tractor frontal ballast had the greatest impact on the front-wheel-based tractor lateral stability, while the rear track width predominantly determined the rear-wheel-based one. Furthermore, an optimal tractor configuration was given by taking into account the stability indexes for both front and rear wheels. The approach provided a reference for tractor stability optimization design and a theoretical basis for further tractor anti-rollover control.