The velocity of agricultural vehicle is an important variable for the navigation system and variable rate applicator in precision agriculture, and the stable velocity in the filed improves the control accuracy of those systems. After analyzed the powertrain system of agricultural vehicles, a simple and general velocity control system was designed regardless of the structure of powertrain. Meanwhile, this system can be adapted without damage the vehicle’s original mechanical structure, and cooperate with the precision agriculture application via the CAN bus. The variable universe method and incomplete derivation control strategy were introduced in the designed of fuzzy-PD controller to improve the adaptability. The road test was accomplished on LOVOL TA800 tractor and YAMMAR VP6 rice transplanter. The test results show that the mean absolute error is less than 0.045 m/s, and the velocity control system is reliable and effective.