In this paper, the kink modes of the plasma in a tokamak with parallel NB injection have been studied. The fast ion component of the plasma has been modelled by a mono-energetic ion beam. Negleiting the dissipative process, an energy principle could be derived from the Vlasov equation in low frequency and small Lamar-radius limit. It is found that none of the entemal kink modes (m≥2) are influenced by the ion beam in the thintorus approximation. But the existance of the fast ion component has changed the kink modes (m = l). Obviausly, by proper choice of the velocity profile of ion beam m = l, n=2 modes can be stabilized absolute. The behaviour of the m/n =1/1 kink mode is very complicated. It could be stabilized or destabilized depending on the beam energy βb, axial safety factor q(0) and radial velocity profile of the beam. A numerical culculation shows that when q(0)<0.924 and the beam velocity profile is properly chosen, the m/n = 1/1 mode can also be totaly stabilized.