A measurement error was caused by using the kingpin turning angle in place of the wheel turning angle in agricultural vehicle guidance. A relation model between the wheel turning angle and the kingpin turning angle was established to compensate the measurement error. Then, a simulation was carried out, showing that the error between the wheel turning angle and the kingpin turning angle increased with the increase of the kingpin inclination. Next, a test was conducted to verify the correctness of the model, and the results showed that the model improved the accuracy of measurement for the wheel turning angle. The mean error decreased by 0.48°, and the maximum error decreased by 0.71°after model compensation．Finally, in practical application, the proposed model improved the performance of agricultural vehicle guidance system.