Virtual reality system is not restricted by place and space, and the virtual situation can be changed flexibly, and have characteristic such as being convenient and safe. Its usually apply such as ' entertainment ' or ' simulated training ' ,etc.. The composition element of the virtual reality system has: Operator, audio-visual system, joystick, motion simulator. This article will make use of above-mentioned components to make our interactive motion simulator. We will discuss how to plan its trajectory, and a research how we can transform the motion of reality space into the motion of unlimited virtual space.