In this work, we investigated the adsorption behaviour of sulfur dioxide on pristine and Au dimer decorated gamma-graphyne (gamma-GY). From comparing the adsorption energy, electron transfer and band gap, the most energetically adsorption configurations were gained. Then we made a further discussion of charge density difference, electron localization function (ELF), band structure, density of states (DOS) to evaluate the chemical and physical interactions between the SO2 and the gamma-GY. The results indicated that the SO2 adsorption on the pristine gamma-GY just exhibited van der Waals force with very weak chemical interactions. But SO2 could be adsorbed on Au dimer decorated gamma-GY with relatively stronger chemical interactions due to the larger adsorption energy, larger electron transfer, the obvious change of SO2 molecular orbitals and many hybridizations between the Au and the S atom in DOS. Because of the unchanged band gap of Au dimer decorated gamma-GY, it is more suitable for Au-2-GY to be applied in QCM gas sensor to detect SO2 rather than resistance type gas sensor.