In this paper, the variation laws of alkalinity and mechanical properties of vegetated concrete with CO2 curing pressure were investigated, and the effect of CO2 curing pressure on the reaction rate and product generation was discussed by combining X-ray diffraction quantitative phase analysis (XRD-QPA), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show that increasing the CO2 curing pressure can improve the carbonation rate of tricalcium silicate (C3S), dicalcium silicate (C2S) and calcium hydroxide (CH). At the same time, the carbonized dense layer can be generated rapidly, which is conducive to delaying the generation and leaching of CH. The calcium carbonate (CaCO3) and hydrated calcium silicate (C-S-H) gel generated by the carbonation reaction increase the cement stone compactness and effectively improve the compressive strength of vegetated concrete. Compared with normal pressure CO2 curing, the 3 d compressive strength of vegetated concrete cured under CO2 curing pressure of 0.3 MPa for 1 h increases by 72.8%, the 28 d compressive strength increases by 4.8%, and the 28 d pH value decreases from 11.4 to 8.2. Moderately increasing the CO2 curing pressure is effective in reducing the alkalinity and increasing the strength of vegetated concrete.