The study is devoted to the evaluation of vibrational relaxation times in carbon dioxide using the kinetic theory methods. There are several relaxation channels in CO2, such as vibrational-translational energy transitions within modes and vibrational-vibrational exchanges between different modes. The theoretical expressions for the relaxation times of such processes are derived; they depend on the energy variation in a specific collision and cross sections of corresponding transitions. The first-order perturbation theory as well as two modifications of the forced harmonic oscillator (FHO) model are implemented for the transition probabilities. Relaxation times are evaluated in the temperature range 500-10000 K; it is shown that they are strongly affected by the cross section model. It is found that the FHO model provides good agreement with experimental data at low and moderate temperatures; at high temperatures, both models give non-monotonic trends for the relaxation times. The reasons of such behaviour are analysed.