Abstract: The causes of salinization of medium and its effects on seedling-growing in float system were studied.The results showed that the degree of salinization of medium was closely related to the temperature, humidity and electroconductivity (EC) of medium during seedling growing process;salinization resulted in low emergence and seedling rate and poor seedling quality.The effects of the salinization of medium could be effectively decreased by reducing the content of salts in medium and keeping the EC(25℃) of its saturation extract ≤ 1160μs/cm.