The effects of potassium on the lengths, number and some physiological characteristics in root system and the economic propcrties of the spike were studied in early maturing rice breed（Guang-lu-ai 4） under the condition in mud-pot. The growths of the root system and the intensity of bleeding sape were increased when the potassium was used in high level of nitrogen. The results were in concordance with the change of the ratio on free-water content to bond-water in roots by using potassium. Some different results were obtained when potassium was used in different levels of nitrogen. Total amount of nitrogen in root decreased when high level of nitrogen was used, but the accumulated nitrogen increased adversely in low level of nitrogen was used. Furthermore the number of cytochrome oxidase bands could be led to change when potassium was used in high level of nitrogen. Favourable economic properties were obtained in spike potassium was used either in high or low level of nitrogen.