An ultrasonic distance measuring based row guidance method is presented to guide a robot platform which is designed independently to drive through the row crops in a field. The offset of the robot platform are detect-ed real-time for guiding the robot inside the crop row and also turn at the end of the rows to adjacent row au-tomatically. Preliminary experiments of row guidance were implemented in rose field. Experimental results show that algorithms of row guidance and headland turn are according to the parameters measured and ana-lysed such as the offset for row guidance and the difference between the motion trajectory of the robot and the expected trajectory. The accuracy of row guidance is ±70mm at the speed of 1 m/s. Tractacus got the 3rd place at free style category of Field ROBOT Event 2012 with smart spraying application which is starting to spray only if it sees the crop canopy.