Abstract: Maize is a crop with low protein. Increasing protein content and grain yield of maize has become a focal concern for maize cultivation. Applying plant growth regulator (PGR) to regulate carbon metabolism and nitrogen metabolism of maize may be a promising approach to increase protein resource. A field experiment was conducted to compare the (effects) of PGRs with different formula on the photosynthesis characteristic and nitrogen metabolism of maize. The results showed that PGRs significantly increased the chlorophyll contents and the net photosynthetic rate of functional leaves, the transportation of nitrogen from leaves and stems to grains, the activities of nitrate reductase, glutamine synthetase and glutamine transferase in functional leaves of maize and glutamine synthetase and glutamine transferase in grains of maize in grain filling stage, and the activities of protease in maize functional leaves in the middle and anaphase of filling stage. The grain yields, the protein contents in the grain, and the grain protein yields were significantly increased when maize plant was treated with PGRs. PGR4 and PGR3 had the best feedback effects. The protein N in maize grain, maize grain yields and grain protein yields of treatment PGR4 were increased respectively by 1.35 g/kg, 9.5%, 19.6% compared with CK. The protein N in grain, grain yields and grain protein yields of PGR3 increased by 0.78 g/kg, 11.4%, 17.4% compared with CK respectively.