Abstarct: The gas sensor is a sensing device able to measure target gas molecules in a given environment. Graphyne -baxsed gas sensors have received special attention in recent years. Graphyne is a type of graphene in which the hexagons of graphene are connected by an acetylene bond. It is available in three types of graphene alpha, beta and gamma, the most common form of which is gamma Graphyne. In this research, the physical properties of adsorption of CO, CO2, Cl2, F2, O2 molecules on gamma Graphyne nanosheet have been studied using density function theory (DFT) and van der Waals approximation (VDW) using the SIESTA computational code. The gas molecules are optimized in both horizontal and vertical positions at a distance of 2 to 3 angstroms from the Graphyne sheet. After optimizing the adsorption energy, the electronic structure, the equilibrium distance after molecule adsorption, and the amount of charge transfer and band gap changes are calculated. It was observed that the gamma Graphyne band gap has slightly changed after the adsorption of gas molecules and remains semiconductor. Chemisorption occurred for F2 and O2 molecules and physisorption occurred for CO, CO2 and Cl2 molecules. The amount of transfer charge in Chemisorption was higher than physisorption.