In order to solve the problems of weeding robot including the flexible movement in field and removing weeds without injuring crop seedlings, the principle of intelligent weeding robot system and the mobile robot platform were studied. The mobile platform was a four-wheel driven and four-wheel steering robot. It could move within the speed of 0~1.5 m/s and each leg could rotate freely around Z-axis of itself. A three-finger manipulator was also designed. All the three fingers could rotate around their public-axis and one of them could also around its own Z-axis. When the robot worked, based on the location information of seedlings and weeds gotten by the machine vision, the rotation speed of movable finger could be controlled to avoid injuring the seedlings while the two fixed fingers would remove the weeds between two crop seedlings continuously. The simulation of the trajectories of three-finger manipulator showed that more than 90% weeds could be removed when a manipulator was installed on each side of crop rows.