Abstract: Abstract: To improve the water use efficiency of artificial light greenhouse, on the basis of the semiconductor refrigeration and the theory of air dew-point, the water transpiration by plants in greenhouse is condensed, which meets the requirement of the indoor dehumidification and recycling for irrigation. The studying object is potted pepper. The experimental period is from May 7 to July 4 including the growth period, the flowering period and the fruiting period. The experimental greenhouse is an airtight greenhouse designed with glass in this paper, whose size is 2 000 mm × 600 mm × 1 200 mm. The red light emitted by LED (light emitting diode) is used as the light source of photosynthesis, with 650 nm wavelength and light intensity of 400 μmol/m2•s. The experiment of potted pepper culture was conducted in greenhouse, and outdoor controlled trials were conducted. The cavity with a diameter of 16 cm was opened on the side wall of the greenhouse, and the 250 cm aluminum foil tube is used to connect the condenser box and the cavity. The aluminum foil tube forms a closed loop pipe equipped with a duct fan, which can carry out air circulation. The results show that the working temperature of the semiconductor refrigeration aluminum plate is 5.5 ℃, which corresponds to the temperature range of 7-18 ℃ in sealed space. In the closed greenhouse, the semiconductor refrigeration is opened and the natural convection and forced convection are designed. The convection test was carried out in the greenhouse. The average humidity is 76% for the natural convection and 53.8% for the forced convection, which can meet the requirement of dew-point dehumidification. In the growth phase test, the forced convection air inlet is adopted to dehumidification. In different periods, the temperature range of closed greenhouse is from 18.6 to 28.2 ℃, and the dehumidification effect is significantly improved with the temperature increasing. The amount of irrigation in the development period and the flowering period shows a steady upward trend from 132 to 201 mL, indicating that the plant transpiration is small. The recovery in the same period is also in a steady upward trend from 35 to 101 mL, with an average recovery rate of 26.3%. In the fruiting period, the amount of irrigation increases to 540 mL. With the increasing of the ambient temperature and plant growth demand, transpiration is increased. In the same period, the daily recovery is 375 mL, and the recovery rate is 69.4%. Observing the physiological changes of potted pepper indoor and outdoor, the plant height, stem thickness and singe leaf area of the former are significantly different from the latter. In this paper, the artificial closed greenhouse uses semiconductor refrigeration to condense water evaporated and spread by plants. The effect is remarkable. And the irrigation of the potted pepper can use recycled water to realize the normal growth in closed greenhouse.