Abstract: Weld forming,tensile properties,fracture characteristics,hardness characteristics and microstructure characteristics of joints were studied under different heat inputs by laser-arc hybrid welding. The results showed that,under conditions of the experiment,the heat input of+ 7 mm defocus was 1. 6 times as much as that of + 5 mm defocus,and welds became wide under high heat input. The back width of welds under + 7 mm defocus was 1. 2 times that of welds under + 5 mm defocus. Tensile properties of joints decreased,tensile strength of + 5 mm defocus and + 7 mm defocus was 88% and 82% of the base metal respectively,and elongation after fracture was 96% and 48% of the base metal respectively. Under high heat input,dimples at the fracture were relatively shallow and microhardness decreased. Precipitated particles in weld and fusion zone were more,fine and dispersed under lower heat input,while they were less and coarse under higher heat input,namely they gathered and grew up.