A preparation process of atomically precise nine-nuclear silver nanoclusters (Ag9-NCs) fluorescent nanotube and its application in the detection of arginine (Arg), the fluorescent nanotube is formed by supramolecular self-assembly of Ag9-NCs and peptide (DD-5); the fluorescent nanotube prepared by the present invention has good luminescence performance due to its highly ordered structure, the quantum yield is 8.11%, and the fluorescence lifetime is 6.10 μs; after adding Arg, the highly ordered structure is destroyed, resulting in fluorescent quenching; the preparation method of the Ag9-NCs fluorescent nanotube of this invention is simple, the cost is low; at the same time, the detection method is fast and easy to observe.