In order to clarify the effects of nitrogen fertilizer and planting density interaction on rice yield and dry matter accumulation under salt-alkali conditions in cold region, Longgeng 21 was used as the material to conducted experiment. The results showed that rice yield had a significant quadratic relationship with nitrogen fertilizer and planting density. Under the saline-alkali conditions, the single-factor nitrogen application rate and planting density of Longgeng 21 were 169.9±5.0 kg/hm² and 32.9±1.0 clumps/m², respeclives. The interaction of moderate nitrogen application and higher planting density was more likely to obtain high rice yield. The combination of high nitrogen fertilizer and high planting density could obtain higher dry matter accumulation and LAI while the yield was significantly reduced at the full heading stage. The combination of medium nitrogen fertilizer and medium planting density could obtain higher photosynthetic rate of flag leaves at the full heading stage, thereby increasing rice yield. The combination of high nitrogen fertilizer and high planting density was more likely to receive more numse of spikes, but the combination of medium nitrogen application and low planting density was easier to obtain larger spikes. There was no interaction effect between nitrogen fertilizer and planting density on thousand-grain weight. Therefore, it is necessary to scientifically and rationally cooperate with nitrogen fertilizer and planting density to build a reasonable group structure, and thus rice yield potential in the saline-alkali land of cold regions can be realized.