Carbonation curing was adopted to accelerate the hydration of foam concrete with lower density of around 450 kg/m3. After standard curing in mold for 2d, the foam concrete samples were marked into two groups. The first one is directly cured in ‘Carbonation Test Chamber for Concrete’ with CO2 concentration 20%, RH 70% and temperature 20°C (it was called ‘carbonation curing’) for 3d to 56d. The second one is cured in ‘Standard Curing Room for Concrete’ with RH ≥95% and temperature 20°C (it was called ‘standard curing’) for 7d, and then at carbonation curing for 3d, 7d and 21d. The strengths of harden foam concrete were tested, the hydration products were analyzed by means of XRD and TG/DSC. The results were compared with those of standard curing samples. It indicates that foam concrete with lower density is easier to be carbonated; the hydration of both C3S and C2S accelerates by carbonation curing, which results in higher early strength improvement. Vaterite is popular in the second group of samples, while it only appears in the first group of sample with longer carbonation time of 56d. Vaterite was considered to be formed from the further carbonation of CxSHy.