Aiming to define the effect of nitrogen fertilizer reduction on nodal root endophytic fungal communities of summer maize by using the method of Illumina Miseq high-throughput sequencing. Based on farmers’ practice for N fertilization, four treatments, i.e. 270kg/hm2(CK: 0%), 243kg/hm2 (N1: -10%), 216kg/hm2(N2: -20%) and 189kg/hm2(N3: -30%) were applied. The results showed that the effects of N fertilizer amount reduction by 10%~30% on diversity index Chao1 of aboveground nodal roots were not significant, and the amount of N fertilizer reduction by 20%~30% increased significantly Chao1 index of underground nodal roots. The effects of amount of N fertilizer reduction by 10%~30% on the diversity index Shannon-Wiener index of aboveground nodal roots were noticeably increased, while the same index of underground nodal roots were noticeably decreased. N fertilizer amount reduction by 10%~30% increased significantly the abundance of Pleosporales in aboveground nodal roots, and increased significantly the abundance of Ascomycota, Sordariales and decreased significantly the abundance of Hypocreales and Xylariales in underground nodal roots. N fertilizer amount reduction by 10% increased significantly the abundance of Glomeromycota in nodal roots, and N fertilizer reduction by 30% only increased significantly the abundance of Glomeromycota of underground nodal roots. With the increase of proportion of nitrogen fertilizer reduction, the similarity coefficient was deceased gradually with CK treatment. The correlation analysis showed that grain number was significantly correlated with the abundance of Pleosporales of aboveground nodal roots, and the abundance of Glomeromycota and Hypocreales of underground nodal roots. Efficient spike number was significantly correlated with the abundance of Sordariales of underground nodal roots. By comprehensive comparison, the effect of amount of nitrogen fertilizer reduction by 30% on nodal root endophytic fungal communities was better than that of other treatments. Compared with CK treatment at the filling stage of summer maize, the abundance of Pleosporales of aboveground nodal roots was significantly increased by 809.95%;and the abundance of Glomeromycota and Sordariales of underground nodal roots was significantly increased, while the abundance of Hypocreales was significantly decreased by 78.14%.