The present invention discloses a nitrogen-doped carbon quantum dot detection paper and its preparation method and application. The nitrogen-doped carbon quantum dot detection paper of the present invention is made of the following mass percentages of raw materials: cellulose: 9%-50%; amino acids: 50%-91%. The preparation method of the nitrogen-doped carbon quantum dot detection paper of the present invention comprises the following steps: first dispersing the cellulose and amino acid in a solvent, then carrying out microwave reaction, filtration and drying, and obtaining the nitrogen-doped carbon quantum dot detection paper. The nitrogen-doped carbon quantum dot detection paper of the present invention can be used to detect whether the metal cations in the wastewater exceed the standard. It has the advantages of high luminescence intensity, good color, fast detection speed and good stability, and its preparation method is simple, green and environmental friendly, and it is suitable for large-scale promotion and application.