Abstract: The water-holding and water-keeping capacity of media is important restriction factors because of apply of soiless seedling nursery in plug tray which nutritional area is small. The experiment which applied two water retention agents and three kinds of concentrations studied the water-keeping capacity of media and influence of seedling quality in plug seedling nursery. The result shows:T3（XIWOTE4‰）which is highest concentration is 2.400g media and T6（KEHAN4‰）2.475g after holding water, but CK is only 2.250g. The rate of losing and water-keeping capacity is the same principle. Water retention agent can solve the problem the contradiction between the water need and water supply when soiless seedling nursery is done. But higher concentration treatment is bad for seedling quality. The seedling quality of KEHAN2‰ is best on condition of the experiment.