Abstract: Orthogonal experiment design was taken for the research of the interactions among temperature, pH and N/P ratio and their inhibitory effects on Microcystis aeruginosa. The results showed that reed extract led to gathering in algae cells, and its effects on algae cells and the density of Microcystis aeruginosa cells and the variation of amount of chlorophyll a were both relative to the three above-mentioned factors. Temperature was the major factor affecting the inhibitory effect, and then were pH and N/P ratio. There were also interactions between temperature and N/P ratio. But there was no distinct difference between pH and N/P ratio. The specific phenomena were that the low temperature group (10℃) showed the most distinctive inhibitory effect, the inhibitory effect declined with the temperature rose, and the pH and N/P ratio were both closely connected with the temperature in their inhibitory effects. Levels of temperatures of all low temperature groups (10℃) and temperatures, pH and N/P ratio of most medium temperature groups (18℃) were distinctly different from those of the high temperature groups (25℃) (P0.05). According to various analysis the best condition for reed extract's inhibitory effect on M. aeruginosa was at 10℃, pH value equals 9 and N/P ratio equals 2.Seven days after continuous cultivating under such environment, the density of algae cells decreased to 40.48%, and the chlorophyll a content decreased to 51.26%. This result showed that reed stalk lixivium was effective to reduce the chance of algal bloom happening and helpful in recovering from blue-green algae pollution.