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【Objective】The experiment was conducted to study the effects of different nitrogen application rates on enzyme metabolic activity and yield and quality of spring maize grain under 90 000 plant·hm-2 super-high planting density.【Method】The experiment was carried out at the experimental base of Northeast Agricultural University.Dongnong 253 was used as material.Four treatments were set up(0,195,279 and 362 kg·hm-2,designated as 0-N,70-N,100-N and 130-N,respectively),with a density of 90 000 plants per hectare.【Result】The activities of ADPG,SSS and GBSS increased first and then decreased with the increase of nitrogen application,and reached the highest level under 100-N treatment.With the increase of nitrogen application rate,the crude starch,crude fat and crude protein content in maize grains increased first and then decreased,all of which were the highest under 100-N treatment.The yield of 100-N treatment reached 11 047.68 kg·hm-2,which was significantly higher than that of other treatments.【Conclusion】100-N application could effectively promote the activity of key metabolic enzymes,improve grain quality and increase yield under super-high-density planting in Heilongjiang Province.The study provided theoretical and experimental basis for increasing density,reducing nitrogen and improving quality and yield in maize planting in Heilongjiang Province. [ABSTRACT FROM AUTHOR]