Abstract: Abstract: According to building structure and temperature variation of solar greenhouse wall, a two-dimensional steady flow and heat transfer model and a one-dimensional unsteady heat conduction model were established for simulation and study on the thermal performance of an air enclosure covered with aluminum foil, to explore suitable structure of the air enclosure in solar greenhouse wall insulation design. The results revealed that the wall surface covered with aluminum foil could effectively reduce radiation heat in the air enclosure; thermal resistance in the air enclosure increased with the rise of the enclosure height, and when the height reached 1.5 m, thermal resistance tended to be the same; when the enclosure thickness was less than 0.03 m, the air inside enclosure was in the stationary state, with heat conduction and thermal radiation as main heat transfer way, thermal resistance increased with the increasing thickness; when the thickness was more than 0.03 m, air natural connection in the enclosure was enhanced continuously, so convective heat transfer gradually replaced heat conduction, thermal resistance decreased with the increasing thickness. In wall insulation design of solar greenhouse, the suitable height and thickness of air enclosure covered with aluminum foil were 1.5 m and 0.03 m respectively. When temperature difference between inside and outside surface of the enclosure was 2-10 K in the simulation of heat preservation layer, average thermal conductivity was 0.047 W/(m· K), and thermal resistance was 0.70-0.58 K·m2/W in the air enclosure, heat preservation and heat insulation effect was equivalent to 0.81-0.67 m thickness of solid clay wall, or 0.55-0.45 m thickness of red brick wall, or 0.20-0.17 m thickness of coal cinder, or 0.06-0.05 m thickness of pearlite, or 0.03-0.025 m thickness of polystyrene board; When temperature difference was 10-20 K in the simulation of thermal conductivity layer, average thermal conductivity was 0.052 W/(m·K), and thermal resistance was 0.60-0.55 K·m2/W in the air enclosure, heat preservation and heat insulation effect was equivalent to 0.70-0.64 m thickness of solid clay wall, or 0.47-0.43 m thickness of red brick wall, or 0.17-0.16 m thickness of coal cinder, or 0.06-0.05 m thickness of pearlite, or 0.025-0.02 m thickness of polystyrene board. There are two types of solar greenhouse wall structures: 360 mm thickness of red brick wall + three 30 mm air enclosures covered with aluminum foil +120 mm thickness of red brick wall, 240 mm thickness of red brick wall + three 30 mm air enclosures covered with aluminum foil +240 mm thickness of red brick wall. The heat released to inside greenhouse form the two walls greatly increased than 480 mm thickness of red brick wall, but was not significantly different from the wall of the same structure composed by red brick wall and polystyrene board. Polystyrene board can be replaced with enclosure of this suitable structure in solar greenhouse wall design.