Abstract: On the basis of the theories of solar engineering and net-work optimal method, the authors analysed the light transmissivity of sunlight greenhouse. At first,a model to monitor the solar energy was presented. By using the model , an optimal function for light transmissivity into sunlight greenhouse was set up, and a computer programme solving the function was realized. Calculated results showed that the light transmissivity was 58808 kJ/day into 5m span sunlight greenhouse,and was 300 kJ/day higher than that of the greenhouse of the same span designed by the traditional optimal methods.