Abstract: Abstract: A water circulation system of pipe network formed by roof truss for heat collection and release was developed to enhance the indoor temperature at night in Chinese solar greenhouse. This low-cost solar-utilizing system was a pipe network formed by top and bottom booms of roof truss and water could flow in it. The pipe network was used as a solar heat collector in the daytime and a radiator in the evening. In the daytime, when the surfaces of pipes absorbed solar radiant heat and their temperature became higher, the heat could be collected by the flowing water in pipes and stored in an insulated tank. In the evening, when the indoor temperature of greenhouse became lower, the heat stored in the tank could be released into greenhouse by the flowing water in pipes. Theoretical calculation showed that the solar energy interception rate of the pipe network could reach 7%-8% when the spacing of roof trusses was 1 m, and the diameter of boom pipes was 33.5 mm, and that the water in tank could store the heat absorbed by pipe network for 2-3 d when the cubage of tank was 1.5-2.5 m3/100 m2 (greenhouse floor area). A winter experiment was conducted in a solar greenhouse with the floor area of 620 m2 in Beijing. The pipe network consisted of 68 roof trusses with the spacing of 1 m, and both top and bottom booms were made of steel pipes with the inner diameter of 25.7 mm and the outer diameter of 33.5 mm. The effective cubage of the tank was 8.6 m3. When the system of pipe network was operating, the water in the tank would be pumped into the top booms and then flowed into the bottom booms, and finally it returned to the tank. The system would be operated for heat storage when the indoor temperature of greenhouse became over 20 ℃ in the daytime, and for heat release when the indoor temperature of greenhouse became below 10 ℃ in the evening. The results showed that the average rise in the temperature of the water in the tank was 4.7 ℃, the average thermal storage capacity was 149 MJ, and the average thermal storage flux was 8 721 W in the daytime, and that the average drop in the temperature of the water in the tank was 2.5℃, the average heat release capacity was 78.9 MJ, and the average heat release flux was 5 974 W in the evening. Compared with a control solar greenhouse, the minimum daily average indoor temperature in the test greenhouse was improved by 2.4℃ at night. The water circulation system of pipe network is formed by the greenhouse's own roof truss, and therefore it consumes less extra materials, its manufacturing cost is lower, and it has not any impact on the greenhouse production space. Moreover, it has the advantages of simpler operation, lower operating cost, easier maintenance, and so on.