With the development of nuclear power industry, the heavy section stainless steel vacuum vessel presents many challenges to joining methods. The conventional welding processes can’t satisfy the strict accuracy and quality requirements due to its higher heat input. In this paper, a 3500 W Slab CO₂ laser and a 20 kW fast axial flow CO₂ laser were applied to weld austenitic stainless steels with a plate thickness over 10 mm. The autogenous laser welding, narrow gap laser welding with filler wire and laser-tungsten inert gas (TIG) hybrid welding with filler wire were exploited respectively. Meanwhile, the joint microstructure and properties were studied. The experimental results shown that welds with good appearances and no holes and cracks could be obtained with laser beam welding techniques, and the joint microstructures and properties are satisfied with the service requirements.