The cycloaddition reactions of NH to different bonds on C70 have been studied by the first-principles calculations. The results indicate that the reactivity of cycloaddition reactions is determined by the directional curvature, KD, and the larger binding energy of Eb on the bond C5–C'5 can be ascribed to the unique bond which can be treated as the shortest bond of (5.5)-SWCNT in the four [6,6] ring fusion bonds. This work also discloses that the energy gap of different spin states is decided by the electronic density, and that of the frontier obitals for the bond C5–C'5 is larger than the value for the C4–C'4 bond. Furthermore, the transition state investigation of the two bond addition reactions provides a reaction barrier of 11.10 kcal/mol for the NH cycloaddition to the C5–C'5 bond; whereas, the addition reaction on C4–C'4 is a spontaneous pathway. Herein, the dynamics effect illustrates the [2+1] cycloaddition reaction on the equatorial C5–C'5 bond to be unfavorable.