The supercritical and subcritical CO2 fluids are both new technologies having good industrial applications such as cleaning with the advantages of no residue, recyclability and so on. The technology of ultrasound coupled with them can enhance the dissolution and improve the mass transfer. However, there is a lack of in-depth study of its mechanism. The reasonable mechanism analysis of enhancement is stated in this paper. A new model is proposed that can simulate the dynamics of cavitation bubbles in the subcritical CO2 fluid based on the Rayleigh-Plesset equation. The effects of different parameter conditions on the dynamics of cavitation bubbles have been discussed and ideal parameter conditions which are beneficial to the dissolution are also listed from the dynamical simulation results.