Based on the designed structures, the calculations of geometry optimization are performed in first principle theory VASP code. After full geometry optimization, the structures of Ti3AlB2 and two designed Ti2ZrAlB2 keep their symmetry as shown in Figure 1. And the calculated equilibrium structural data and the bond lengths are listed in Table 1. For two Ti2ZrAlB2 structures, it is easy to understand that the bond lengths of Zr-B and Ti-B are different. But for Ti3AlB2, the bond lengths of Ti(1)-B and Ti(2)-B are different, and the former is slightly longer than the latter. Similar phenomena have been found in Ti3AlC2 and Ti3SiC2 [33-34]. Ti3AlB2 can be regarded as formed by introducing Al element into Ti-B compound. The introduction of this element changes the bonding environment of Ti atom, and it leads to the increase of partial bond length and the decrease of partial bond length of Ti-B bond in the structure. Thus, two types of Ti-B bonds with different bond lengths appeared in Ti3AlB2 structure.