Projection displays are widely applied as tools for multimedia in conference room presentation, education center, R&D center and more places. To provide a more interactive environment, a new kind of human-computer interactive device is designed and presented. A two-dimensional CCD is the sensor of the unit. Through optical filter, CCD exports full video signal including a series of isolated positive pulse caused by the specific light-spot target generated from a specific light-pen. Through a video sync separator, combinational logic and sequential logic process of the full video signal, the target image's two-dimensional position on the light sensitive layer of CCD can be gained. The specific light-pen also sends the function logic message to the controller part through wireless communication. A microcontroller will combine the position information and function message, and then send it to computer through RS-232 of USB interface. The software in computer will process these messages. The specific light-spot's relative coordinates in the projection screen is gained. With the coordinate and the function message, the software will drive the computer to implement certain functions. With the specific light-pen, one can control the computer, take notes and shape his desire in the screen. Now the device is applied in LCD projection displays and it also can be applied in any large screen display. With the improvement of the system and the software, the function will be more powerful and provide a more interactive human computer interface (HCI).