The low-power laser-TIG hybrid welding technology was used to test the based welding of the 15 mm and6 mm TC4 titanium alloy fillet structures. Analyze the difference in weld formation of fillet joint structures of unequal thickness plates with different welding parameters,typical microstructure characteristics and microhardness distribution of welded joints.The results show that the best welding joint is obtained when the laser power is 485 W,the TIG arc current is 240 A,and the reserved gap is 0.3 mm;the matching use of the laser and arc allows a wider range of welding parameter choices,which enhances welding adaptability to special structures. The joints of unequal-thickness plate of titanium alloy have asymmetric joints after welding. The microstructures on the two sides are different and the grains on the thin plate side grow significantly and columnar grains appear. The basketweave structure in the TC4 α-β titanium alloy after welding can improve the strength of the weld.