Applying a guarantee effectiveness simulation assessment method to combine harvester cross-zone operations improves the guarantee capability of the combined cross-zone operations. A combined harvester cross-zone operational simulation model was designed based on the Simlox simulation platform. The structure of the combine harvester and elementary mission characteristics of the cross-area operation were combined. Typical indicators for the simulation evaluation of guaranteed effectiveness were defined, and the simulation process, sampling, and statistical methods were determined. Operation availability (Ao) and mission completion probability (Pmcs) are the leading indicators for assessing the capability of the combine harvester in cross-zone operations. The analysis of the simulation results shows that the significant factor affecting the guarantee capability of the combine harvester is the shortage of spare parts for the unrepairable units (DU) after an equipment failure and that the guarantee capability can be optimized in the direction of the spare parts inventory. This study establishes a simulation model of the combine harvester cross-zone operation guarantee, which can be used to evaluate the guarantee capability of the combine harvester cross-zone operation and provide a reference for optimizing the guarantee model of the combine harvester cross-zone operation.