Based on magnetoelastic effect, the magnetic circuit of the draft sensor, which was used in electro-hydraulic lifting mechanism of high-power tractor, was learned and designed. According to the analysis of the working condition and the structure of the same type product abroad which used a columnar excitating magnetic core to create the working magnetic field, a new kind of magnetic structure was designed, which changed the excitating magnetic core from columnar to cruciform, so that changed the mechanical dimensions from 2D to 3D. For the design, bear force from horizontal and vertical directions in the same time, which resulted in the shear deformation in both directions, it also made greater change of the magnetic field, and it is more comfortable under actual working conditions. The 3D model was built to show the structure of the draft sensor with cruciform excitating magnetic core, and the mathematical model was built, which could describe the operating principle and working process of the magnetic circuit in detail. Then according to the mathematical model, the simulations of two kinds of draft sensor were made by Matlab/Simulink. By comparing the two simulations, the result showed that the linearity of this new design with a cruciform excitating magnetic core was changed from 1.85% to 0.08%. And the sensitivity was changed from 0.09mV/kN to 0.21mV/kN, which proved that the new design of draft sensor with cruciform excitating magnetic core was more suitable for the force measurement and control of electro-hydraulic lifting mechanism under the condition of heavy load, which can be more adaptable for bad working environment to improve the tillage effect.