0.02m。 An automatic guidance system was developed on KUBOTA SPU-68 rice transplanter using Trimble 5700 RTK-DGPS and Crossbow AHRS500GA-227. RTK-DGPS positioning data was corrected using the heading, roll and pitch parameters acquired from AHRS500GA. A Kalman filter based on position-velocity model was developed to smooth the corrected DGPS positioning data and evaluate the bias error of the heading angle. A new trajectory tracking control method was proposed based on pure pursuit model. The determination method of the look-ahead distance was studied in detail for line tracking. Simulation result indicated that the optimized look-ahead distance could be determined for a special traveling speed based on the ITAE optimization. The test result showed that the proposed positioning and orientation evaluation algorithm could eliminate the effects of uneven field condition on GPS positioning and evaluate the bias error of the heading angle from AHRS online. The developed trajectory tracking controller was helpful to improve the tracking control performance. The maximal lateral tracking error could be kept within a range of ±0.17 m and the mean lateral tracking error was less than 0.02 m at the normal traveling speed.