Abstract: The theory and structure of optical transmitter/receiver are investigated. Based on the theory of current to light conversion and photoelectric conversion, a free space laser communication system is studied. Problems in the circuit design of optical transmitter are analyzed. The communication between two computers is realized with a transmission speed of 10 Mbit/s and transmission distance of above 1 km. Waveform of experimental results is presented. The system can be used in the point to point communication between two computers.