In this research, we reviewed how to get the relationship of the neutrino oscillation probability in the two flavor approximation, and tested the theoretical model of the oscillation solution. We show that the oscillation probability of neutrino relates with neutrino energy, length of the baseline (the distance between the source and the detector), mixing angle , and square mass difference 2 2 2 1 2 12 m m m . This research shows that in order to occur the oscillation of neutrino, it must be at least one of the mass states different of zero. This means that the relationship 0 2 12 m must be verify. In other words neutrino must have non zero mass. This result holds a huge physical importance. The first regards the Standard Model of elementary particles, which considered neutrino massless. The second regards the OPERA experiment, where neutrino have non zero mass, and cannot spreading fast equal to the speed of light and so this does not agree with the experience of OPERA, which found that the neutrino spreading faster than the speed of light in a vacuum.