Abstract: The effects of different deficit irrigation periods on plant yields, fruit quality and water use efficiency of tomato were studied. It was showed that the fruit qualities under different deficit irrigation periods were different. The earlier the deficit irrigation, the firmer and denser the fruit, and the higher the content of soluable solid content, organic acid, vitamin C of tomato fruit, but the sugar/acid ratio changes little. Fruit amount did not change while per fruit weight reduced. The water use efficiency increased when deficit irrigation treatment started from swelling period or setting fruit period, but decreased from Anthesis period. The beginning period of deficit irrigation was suggested as swelling period of first cluster.