Abstract: In order to investigate the influence of heat input on the microstructure and properties of wire arc additive manufactured super duplex stainless steel, sample tests were conducted by MIG arc additive manufacturing of a sing-wall on a substrate of Q345 low carbon alloy steel, using ER2594 super duplex stainless steel wire 1.2 mm in diameter with different heat inputs applied. The microstructure and mechanical properties of each sample were analyzed. The results showed that when the heat input was increased from 435.6 J/mm to 517.3 J/mm, the austenite content grew from 31% to 43%, which was attributed to the greater heat input and the slower cooling rate. When the heat input was further increased to 599.0 J/mm, the austenite content decreased from 43% to 41% due to the loss of nitrogen content. With continuous increase of heat input (from 435.6 J/mm to 599.0 J/mm), the microhardness was initially decreased and then increased, since microhardness is positively correlated with ferrite content. The sample with a intermediate heat input value (517.3 J/mm) exhibited better tensile performance due to its high austenite content.