Abstract: An experiment was conducted under field conditions to study key enzyme activities, soluble protein (Pro) and free amino acid (AA) contents of functional leaves of peanut with different yield levels. The study aimed to specifically clarify the mechanisms of nitrogen metabolism in peanuts under super-yield conditions. The study showed that from initial flowering stage, nitrate reductase (NR) activity in peanut functional leaves gradually declined under different yield levels. NR activity in peanut functional leaves under super-yield condition was not significantly different from that under high-yield condition. However, NR activity under super-yield condition was higher than that under normal yield condition. Glutamine synthetase (GS) activity in peanut functional leaves followed a similar trend under different yield conditions, with single peak curve and the peak value occurring at pod-setting stage. GS activity in peanut functional leaves under super-yield condition was obviously higher than those under high- and normal-yield conditions. Also GS activity in peanut functional leaves under super-yield condition declined more slowly than those under high- and normal-yield conditions. During the experimental period, glutamate dehydrogenase (GDH) activity in peanut functional leaves was not regular. However, from flower-needle stage to pod-setting stage, GDH activity under super-yield condition was significantly higher than those under both high- and normal-yield conditions. During the study period, Pro and AA contents in peanut functional leaves under super-yield condition were significantly higher than those under high- and normal-yield conditions. It was concluded that the capacity of ammonia assimilation and amino acid and protein synthesis in peanut functional leaves under super-yield condition were significantly higher than those under high- and normal-yield conditions. Moreover, senescence of functional leaves under super-yield condition was slow. This delay prolonged functional leaf span in peanuts.