The method of determining the nitrogen isotopic composition of granites in the northeastern part of China is described. The content and isotopic values of nitrogen released from granite samples by stepwise heating were determined as well. The results showed that the different areas of northeastern China have a great difference in nitrogen content and isotopic composition. Nitrogen released from the granites is 1.64-6.23μL/g, with the maximum at about 600℃; from rhyolite and granophyre is 108.98-755.96μL/g, with the maximum at about 900℃. It is proved that fluid is characterized by heterogeneity in the deep crust of the different areas in northeastern China. The nitrogen isotopic compositions in different ranges of temperatures are weighted. And the nitrogen isotopic values are +9.2‰ to +17.0‰, with a variation range of 7.8‰. The nitrogen isotopic ratios may have been fractionated during degassing and the fluid released from granites is the residual component. The method of determining the nitrogen isotopic composition of granites in the northeastern part of China is described. The content and isotopic values ​​of nitrogen released from granite samples by stepwise heating were determined as well. The results showed that the different areas of northeastern China have a great difference in nitrogen content and isotopic composition. Nitrogen released from the granites is 1.64-6.23 μL / g with the maximum at about 600 ° C; from rhyolite and granophyre is 108.98-755.96 μL / g with the maximum at about 900 ° C. It is proved that fluid is characterized by heterogeneity in the deep crust of the different areas in northeastern China. The nitrogen isotopic compositions in different ranges of temperatures are weighted. And the nitrogen isotopic values ​​are + 9.2 ‰ to + 17.0 ‰, with a variation range of 7.8 ‰. The nitrogen isotopic ratios may have been fractionated during degassing and the fluid released from the granites is the residual component.