Typha angustifoliaL., known as narrowleaf cattail, is widely distributed in Eurasia but has been introduced to North America.Typha angustifoliais a semi-aquatic, wetland obligate plant that is widely distributed in Eurasia and North America. It is ecologically important for nutrient cycling in wetlands where it occurs and is used in phytoremediation and traditional medicine. In order to construct a high-quality genome forTypha angustifoliaand investigate genes in response to high nitrogen stress, we carried out complete genome sequencing and high-nitrogen-stress experiments. We generated a chromosomal-level genome ofT. angustifolia, which had 15 pseudochromosomes, a size of 207 Mb, and a contig N50 length of 13.57 Mb. Genome duplication analyses detected no recent whole-genome duplication (WGD) event forT. angustifolia. An analysis of gene family expansion and contraction showed thatT. angustifoliagained 1,310 genes and lost 1,426 genes. High-nitrogen-stress experiments showed that a high nitrogen level had a significant inhibitory effect on root growth and differential gene expression analyses using 24 samples found 128 differentially expressed genes (DEGs) between the nitrogen-treated and control groups. DEGs in the roots and leaves were enriched in alanines, aspartate, and glutamate metabolism, nitrogen metabolism, photosynthesis, phenylpropanoid biosynthesis, plant-pathogen interaction, and mitogen−activated protein kinase pathways, among others. This study provides genomic data for a medicinal and ecologically important herb and lays a theoretical foundation for plant-assisted water pollution remediation.