The present invention discloses a nutritional and efficient nitrogen fertilizer synergist and an application method therefor. The synergist comprises the following components in parts by weight: 10-60 parts of zinc sulfate, 15-45 parts of disodium octaborate tetrahydrate, 100-500 parts of powdery humic acid, 5-20 parts of beta-cyclodextrin, 1-5 parts of a growth regulator, 1-5 parts of ammonium chloride, 1-3 parts of hydroquinone and 1-3 parts of dicyandiamide. According to the present invention, the synergist can be added into a melt liquid of a nitrogen containing fertilizer for granulation, and can be applied to the outer layer of the nitrogen fertilizer in a wrapping manner or is mechanically mixed with the nitrogen fertilizer to obtain a modified nitrogen fertilizer. The synergist can effectively inhibit the soil urease activity, significantly postpone the nitrogen releasing period, improve the utilization rate of the nitrogen, supplement the medium elements and trace elements that are necessary for plant production, and significantly improve the quality of crops.