In this paper, a crossing dual-light-path laser detection system for visibility by forward-scattering is presented. The measurements of visibility and scatter coefficient are realized through measuring scatter energy in forward 30° direction and transmission energy in straight direction for a 0.81μm laser. The system consists of three parts: optical emitting and receiving system, signal amplifying and controlling system, and displaying system. The optical emitting and receiving system mainly consists of laser diode, collimating lens, extending lens, receiving lens, cut-off filter, narrow band interference filter, and Si-PIN photodiode. The signal amplifying and controlling system mainly consists of voltage amplifier, sample/hold circuit, muti-channel analog switch, A/D converter, and 8031 single chip processor. The display system mainly consists of indicator and printer. The principle and configuration of the system are introduced. At last, the key technologies about stability, precision and optical-electronic interference in the process of measurement are discussed.The solution is proposed.