The superplasticity of Ti-46.7Al-2.2Cr(at.%) alloy was studied by mathematical induction. It is found that Zener Hollomon relative formula and there are serious deflections. According to the true superplastic stress and true strain curves, the deflection values of n=-7.46 and B=1439MPa are obtained, indicating that the limit of n>0 has been exceeded, which needs to be characterized by a negative sign. This shows that it conforms to the principle that the smaller n is, the better superplasticity is, but the problem that it has become a negative number needs to attract the attention of peers meantime B is a better match.