Abstract: New types of ferrite and austenite heat-resistant steels used in supercritical or ultra supercritical boilers have issued challenges to conventional welding techniques.As a reliable and advanced joining technique, laser welding may be one of the promising solutions for the welding of these steels due to the low heat input.A slab CO₂ laser with an output power of 3500 W was applied and the narrow gap laser welding process was adopted with T-HR3C filler wire to weld HR3C tubes of the new type austenite steel with a thickness of 10 mm.The joint microstructure and high temperature lasting strength were investigated.It is found that a sound joint can be obtained by optimizing the process parameters.The microstructures in the weld bead are fine column austenite grains with a few fine equiaxed austenite grains, appear more or less symmetrically along the bead center.The grain size in the HAZ is not obviously coarsening.The micro-hardness in the weld is correspondence with that of the base metal, and no obvious softened zone is observed.The high temperature lasting strength of the laser welded joint in the as-welded condition is distinctly improved compared to that of TIG welding joint with post-weld heat treatment.