Optical fiber communication is gradually replacing the traditional cable communications because of it's high speed and high anti-interference advantages. The optical fiber LAN (local area network) has already been in application recently. This paper introduces a optical fiber LAN build in a four-floor building. The advanced devices such as optical exchange board, fiber-optic LAN adapter are used in the optical fiber LAN. These ensure the LAN high speed, high reliability and high anti electromagnetic interference. This optical fiber LAN has already been applied by Shanghai Funeral and Interment Bureau.