With unequal width structure characteristics of thin-walled blades, single track by variable laser spot based on coaxial inside-laser powder feeding rather than multi-track overlapping is adopted, and the thin-walled blade can be fabricated layer by layer directly. The forming quality of thin-walled blades is investigated by variable laser spot based uniform height and stepped single track. The experimental results show that a uniform height cladding layer with different widths can be got by controlling scanning speed and laser power under the condition with sufficient powder mass flow rate. The growth rate of cladding layers isn′t consistent based on uniform height single-trace cladding layer, and the large ratio of width to height position increases quickly. The theoretical model among layer thickness of Z axis, height of single-trace cladding layer and the section curve order of cladding layer is established, and the stepped single track method is put forward to solve the problem of inconsistent growing height. The thin-walled blade with good forming quality can be achieved. This new method can be provided for forming unequal width blade by laser direct forming with coaxial inside-laser powder feeding.