Abstract: In the welding construction made of different materials,the cooling stage after welding will cause thermal stress due to the mismatch of coefficient of thermal expansion between different materials.Meanwhile,the fillet geometry has played an important role on this thermal stress distribution.In this work,by means of finite element numerical simulation,the effect of fillet geometry on the shear stress distribution in the Al-Al2O3 soldering assembly had been analyzed.The calculating results showed that the optimized geometry of soldering fillet is a concave shape in which the extruding length of the soldering fillet is a little more than the gap height.