The adsorption properties of CH 4 , H 2 S, SO 2 , CO, H 2 O and NO molecules on transition metal-supported SnSe 2 surface are investigated by the first-principles method. The calculation results show that the transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) has the lowest adsorption energy when supporting at the Sn site of SnSe 2 , indicating the system is relatively stable. Also, we find that CH 4 , SO 2 and H 2 O molecules tend to adsorb on Sc-supported SnSe 2 surface, H 2 S and NO molecules prefer to adsorb on V-supported SnSe 2 surface, while CO molecule and Fe-supported SnSe 2 surfaces have strong interaction. And, CH 4 , H 2 S and H 2 O molecules act as donors to provide electrons to the substrate, while SO 2 , CO and NO molecules act as acceptors to gain electrons from the substrate. An analysis of charge difference density and density of states reveals that the adsorption energies of gas molecules are related to charge transfer and orbital hybridization. We hope that this work not only provides a promising sensor material, but also provides a new idea for the rational design of two-dimensional materials.