In order to optimize fragments' shape of warhead with variable thickness for increasing damage power, sand box were used to recover fragments from the shells. The fragments' morphology and fracture modes were observed and analyzed, and metallographic analyses of typical fragment were carried out by scanning electron microscope, the mass distribution of fragments and metallographic pictures were got. The results show that: the area of the tensile shear mixed fracture of the shell is significantly smaller than that of the large end when initiation from the small end. There are micro cracks and holes in the middle of the thickness direction of the typical fragment from large taper shell, which near the large end, and disappear as the thickness decrease. The size and shape of the fragments can be controlled by adjusting the structure and initiation position of the shells with variable thickness.