Aiming at the problem of long-distance laser receiving and alignment, a laser bridge system using large area avalanche photo diode is proposed in this paper, which can be used as the extension of Wide Area Network （WAN）and the connection between Local Area Networks（LAN）. The software of the laser bridge system needs a computer as a server for information processing. The hardware connection is realized through the switch and electro-optic conversion, and based on two-way laser lenses placed in two buildings for transmitting and receiving signal. The distance between the two buildings is about 1 km, and the geometric loss of the laser is about 26 dB/km. By adjusting the relative position of the two lasers until the optical power received is less than -30 dBm, the threshold optical power required is realized, which can perform two-way video communication successfully.