Abstract: The effects of potassium (K) application rates on grain yield, K translocation and use efficiency under supper-high yield conditions were studied in fields. Two cultivars of summer maize (Zea mays L), Denghai 661 (DH661) and Zhengdan 958 (ZD958) were selected as experimental materials. The results show that the grain yield, agronomic efficiency of K and K recovery efficiency are increased at the first, and then gradually decreased with the increment of the K application rates. As applied K increased, partial factor productivity from the applied K is reduced significantly. Simulated by a quadratic curve, the grain yield of DH661 reached its maximum under K fertilizer application rate of K 184 kg/ha, and the ZD958 is under the rate of K 201 kg/ha. For per 100 kilogram grain production, it needs to absorb K2O 2.55 kg for DH661 and 3.20 kg for ZD958 as obtaining the highest yield. K is absorbed mainly before the spinning stage, and K in seed comes from nutritive organ mostly. In conclusion, under this field experiment conditions, the most optimal K fertilizer rate is K2O 180 kg/ha.