| On basis of the seasonal movement of the sun during the operation period of the greenhouses in Tianshui city, a mathematical model for building a greenhouse was set up. The geographic in characteristics of Tianshui and the datas of the main structure of the greenhouse, in recent years were analysed. Under the same height and span, the type of dome-arch structure is the best one to collect sunlight and hold heat. The indexes for building a greenhouse were: greenhouse azimuth at 7°～9°, the gradient of sunlight-intecepting roof at 29 ° ～ 32 °, the elevation of the back roof at 42 ° ～ 45 °, the fastigium height at 3.0 ～ 3.5 m, the span at 7 ～ 8 m, the wall thickness at 0.8 m(top ) ～ 1.0 m(base). A scientific theory basis also had been provided. |