A microcontroller-based greenhouse illumination control system is designed in this paper. The system utilizes the digital light sensor (BH1750FVI) to detect the illumination inside and outside. According to appropriate light range of the different crops, the system can select to block the shading film or open a certain number of complementary lights. This system has automatic control and manual control modes. The automatic control mode can automatically maintain illumination in the desired range according to the selected type of crops in greenhouse. In manual control mode, shading film and light needs to adjust manually. Tests showed that the system can compensate for manual control error and low efficiency defects and has strong practicality.