Abstract: To search for high sensitivity of graphene-based gas sensors for HCN gas,the adsorption and gas sensitivity of hydrogen cyanide (HCN) molecules on pristine graphene (PG) and modified graphene,including single vacancy defect graphene (SVG) and Li,B,N,Mg,Al,S,Ca,Ti,Cr,Mn,Fe,Co,Ni and Pt substitutional doped graphene (XG),have been systematically explored by using first-principles analysis based on density functional theory (DFT).It has been found that HCN undergoes weakly physisorption on PG,BG,NG and SG due to low adsorption energy and large adsorption length,and HCN adsorption failed to cause the change of the density of states near the Fermi level.Therefore,the substrates (PG,BG,NG and SG) are not sensitive to HCN molecule.Although the introduction of single vacancy defect increases interaction between the substrate and HCN molecule,the electronic structure of the system hardly change before and after HCN adsorption.HCN molecule is chemisorbed on LiG,MgG,AlG,CaG,TiG,CrG,MnG,FeG,CoG,NiG and PtG.Among them,LiG transforms from metallic to semiconducting and MnG transforms from half-metallic to semiconducting owning to HCN adsorption,suggesting that the electrical conductivity decreases obviously.However,other substrates still retain original property.Therefore,LiG and MgG are more suitable for HCN detection among all of mentioned substrates.Our work provides theoretical reference to design novel graphene-based gas sensor.