Aiming to the problem of poor tractor performance, the matching bench test of positioning valve input voltage and magnetorheological damper excitation current was done. Based on the matching test, a frequency adjust based control strategy was proposed. Using LabView as the software development platform and PCI6024E DAQ as the core, the semi-active suspension control system was established and validated. The results showed that the reasonable match of positioning valve input voltage and magnetorheological damper excitation current could significantly attenuate the suspension dynamic characteristic response. The semi-active suspension control system could effectively suppress the sprung mass vertical vibration, and improve the tractor performance. 