Abstract: With potted tomato plants in greenhouse as the experiment material, and with the plant under normal temperature as control treatment，we investigated the influence of 80%, 100% and 120% of ET of irrigation amount on the cold resistance and fruit quality of tomato under sub-low temperatures in greenhouse. The results showed that sub-low temperatures reduced the activities of catalase and peroxidase, chlorophyll content, relative content and soluble protein content in tomato leaves, as well as fruit quality significantly; but they increased the relative permeability of cell membrane and superoxide dismutase; under both sub-low and normal temperatures, Vc and sugar content, soluble solids were reduced while the total acidity was increased under the condition of 80% or 120% of ET of irrigation amount. It is proved that 100% of ET of irrigation amount under sub-low temperatures was favorable to plant growth and fruit quality during flowering and fruit-setting periods.