The symmetrized normal mode analysis presented in a previous paper was used to analyze the 11B spin–lattice relaxation of solid calcium borohydride. From the analytical results, the quadrupolar and the dipolar spectral densities and reorientational correlation times of various relaxation interactions were evaluated. Based on the spectral densities, the quadrupolar contribution to the spin–lattice relaxation of 11B nucleus was calculated. As expected from the QCC value of 11B nucleus in solid calcium borohydride, the ratio of the quadrupolar contribution to the dipole–dipole contribution in the 11B spin–lattice relaxation was proved to be higher than 30% at 100°C. The symmetrized normal mode could be a useful method for the interpretation of AX4 spin system containing a quadrupolar nucleus, and thus the determination of the motional parameters of BH4 unit in solid calcium borohydride.