Soybean cultivar ’Changnong 18’ was used as material in the field test.Effects of potassium rate on physiological characteristics,yield and quality of soybean were studied.The result showed that in the whole growth period,chlorophyll content showed a decreasing trend after the first increase.Photosynthetic rate showed double-peak curve and there were two peaks.Dry matter per plant changed as S-shaped curve,and it reached the maximum in the R7 stage.Chlorophyll content and photosynthesis rate of the soybean was increased with the increasing of potassium.LAI,dry matter accumulation,plant height,100-kernel weight and yield of soybean was increased with the increasing of potassium too.But,excessive potassium fertilization decreased these indexes.