Abstract: A new transmission visibility measurement system was introduced. Integrating sphere played an important role in monitoring and receiving light. The white LED light source in this system was modulated by external high frequency pulse signal and demodulated in receiver, which would effectively detach the interference by stray light. Integrating sphere was applied to monitor variation of the light source, which can eliminate the error caused by the instability of light source. The collimation lens and beam expanding lens group makes divergence angle in 1 mrad. The high reflection mirrors increase the optical path in the limited space, which also increases the volume of sample and shorten the baseline of transmission system. Adjusting optical path becomes easy by telescope and integrating sphere. After completion of the system, comparison experiment was made with nephelometer. The result shows that the relative deviation between two systems is less than 4% from 1.7 km to 20 km.