In order to improve the stereo feeling of display system, and generate a screen-free aerial image, a floating display system is established and its applied basic theory and key optical devices are investigated. Firstly, the two main factors of floating display are studied based on the binocular stereo vision of human: the first is the display system can generate a real image, and the second is the real image can be observed by both eyes and the binocular parallax is achieved. Then, based on the analysis of floating display, a display system based on lens is established to verify the feasibility of the theory. Finally, according to the simulation analysis, a floating display system using micro lens array is designed and established. Experimental results indicate that the images are displayed in mid-air without any auxiliary screen, and the aerial images are at least 6.5 cm away from the display system. It verified the analysis of floating display and the design of floating display system.