Abstract: The effect of moisture content of medium on transpiration, fresh matter accumulation and related physiological indexes for potted tomato in greenhouse were studied through setting water supply tension at 10，30，50 and 70 hPa using negative pressure pot device. The results indicate：The moisture content of medium can be accurately controlled and maintained by the negative pressure pot device，moisture contents of medium are 88%，76%，63% and 57% at water supply tension 10，30，50 and 70 hPa correspondingly. In different experimental stages，influence of moisture content of medium on daily transpiration is different. Accumulative daily transpiration of potted tomato is as following：10 hPa treatment＞30 hPa treatment＞70 hPa treatment＞50 hPa treatment. The effect of medium moisture content on fresh matter accumulation is the most significant at 30 hPa，followed by 10 and 50 hPa and the least is at 70 hPa. The effect of water supply tension on yield, water consumption and crop water productivity are extremely significant. 30 hPa is the most favorable water supply tension for potted tomato in greenhouse because of the maximum yield and the fresh matter accumulation.

Key words: tomato, negative pressure irrigation, water supply tension, transpiration, fresh matter accumulation, crop water productivity