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The critical nitrogen dilution curve can be used to diagnose crop nitrogen nutrition. In order to construct the leaf critical nitrogen concentration dilution curve of summer maize based on LAI, the field experiments with different water and nitrogen applications were carried out in Guanzhong Plain from 2018 to 2019. Three water levels (rain fed (RF), deficit irrigation (DI) and full irrigation (FI)) and four nitrogen levels (0kg/hm2, 90kg/hm2, 150kg/hm2 and 210kg/hm2) were set to study the response of leaf critical nitrogen dilution curve based on LAI to different water levels. The quantitative relationship between nitrogen nutrition index (NNI) and relative yield was analyzed. The results showed that the relationship between LAI and leaf nitrogen concentration was power function. The leaf critical nitrogen dilution curve based on LAI under RF was significantly affected by the interannual variation (P<0.05), while the leaf critical nitrogen dilution curve based on LAI under DI and FI was not significantly affected by the interannual variation (P>0.05). The dilution rate of leaf critical nitrogen dilution curve based on LAI under RF was significantly higher than that under DI and FI (P<0.05), but there were no significant difference between DI and FI (P>0.05). The critical nitrogen dilution curves of DI and FI treatments were fitted, and a unified critical nitrogen dilution curve was obtained (R2=0.90, P<0.01). In the range of nitrogen application, NNI was increased with the increase of nitrogen application, and the range was 0.62~1.16. The relative yield of RF treatment was 85% of the maximum yield, and that of DI and FI treatment was over 99% of the maximum yield. Therefore, 75% ETc (ETc is the water demand of summer maize) and 150kg/hm2 of nitrogen were recommended for fertigation in Guanzhong Plain. This results can provide reference for the precise management of water and nitrogen of summer maize in Guanzhong Plain.