In this paper, the adsorption of Hydrogen cyanide (HCN) molecules on metal-doped boron nitride nanotube (BNNT) is studied by using density functional theory (DFT) method. Our calculations indicate that the adsorption energy corresponding to this structure increases greatly. In addition, metal doping changes the charge distribution of the BNNT, which results in various hybrid orbitals. The frontier orbital function distribution of this configuration also changes from being uniformly distributed in the tube to being substantially concentrated around the metal atoms and HCN molecules. The results of this series of studies provide new possibilities for HCN sensor research.