Abstract: In order to automatically real-time monitor and record light intensity, a monitoring system of light intensity for ginseng under forest was designed by using TSL2561 and ATMega16L. The system included one master and ten slavers micro-computers connected by system bus. The the second to the tenth slavers were used to get the light intensity in nine experimental sites, and more locations were measured through five monitoring systems. The real-time control system in the principal computer was designed by using MATLAB software. Through adjusting the sampling period of real-time control system in 10, 20, 30, 40, 50 and 60 minutes, the 30 minutes sampling period was thought as ideal sampling interval which had less measuring points and could better reflect the changes of the light intensity. The whole system has the database function for measuring light intensity of the region, and the results can provide convenience and guarantee for establishing the forecast models of forests light environment and analyzing the variability of ginseng photosynthesis rules.