Abstract: A field experiment was carried out to study the effects of potassium fertilization on yield, quality and key enzyme activities of sucrose metabolism of sweet maize. In this experiment, Dongtian3 and Dongtian4 were utilized as materials, and five treatments of potassium fertilization (K2O: 0 kg, 50 kg, 100 kg, 150 kg, 200 kg per hectare) were designed. The results indicate that the fresh ear yields of sweet maize are significantly increased under the potassium fertilization, and the fresh ear yield of the treatment with 150 kg/ha (K2O) is the highest one among the 5 treatments, which is increased by 14.06% compared with the control treatment. Furthermore, compared with the control treatment, the contents of soluble sugars, sucrose, protein and lysine are improved under the potassium fertilization. The dynamic changes of activities of sucrose synthase (SS, synthesis) and sucrose-phosphate synthase (SPS) are similar to the sucrose content in grains of sweet maize after anthesis. There are positive correlations between activities of the two synthases and sucrose content (P0.05 or 0.01). Therefore, potassium application can increase the activities of SS and SPS, and sucrose accumulation. According to the regression model of fresh ear yield and quality, the optimum amounts of potassium fertilizer (K2O) are 133-140 kg/ha for harvesting the high yield, and 140 kg/ha for the high quality of sweet maize in practices, respectively.