Abstract: Hybrid CO2 laser-metal inertia gas(MIG) welding is an efficient and fast welding method,however,porosity is prone to produce when welding aluminum alloy.In order to analyze the porosity characteristics of aluminum alloy in medium thickness by means of hybrid CO2 laser-MIG welding,10mm thick 5052 aluminum alloy was welded by means of bead weld.Theoretical analysis and experimental verification was carried out.The results show that the heat source space and the back protection cushion block influence the porosity obviously.The porosity rate is minimum when the heat source spacing is 2mm~3mm.Porosity can be effectively suppressed by the back protection of cushion block.