In this paper we analyze the performance of a GPS based human following robot which can follow human in complex terrain such as obstacle or slope environment. The robot recognizes the position of the human from the GPS and forms the movement trajectory of the human. The robot follows the human trajectory by using two different ways: direct and trajectory tracking methods. The direct tracking method is that the robot tracks the current position of the human, while the trajectory tracking method is that the robot traces every position of the human trajectory in order. The performance of the two methods is compared through sets of experiments.