Basic magnesium carbonate was prepared by pressured carbonization method using magnesium hydroxide and car bon dioxide as raw materials.The effects of CO2 partial pressure，reaction temperature，stirring speed and reaction time on the morphology of basic magnesium carbonate were investigated.Meanwhile the influence of microstructure of basic magnesium carbonate on its apparent specific volume was studied. Morphology，phase and thermal decomposition of the product were characterized by SEM，XRD and TG -DSC.Results showed that the optimized condition was as follows：partial pressure of CO2 was 0.6 MPa，reaction temperature was 90 ℃，stirring speed was 200 r/min and reaction time was 2 h.Under the optimal con ditions，basic magnesium carbonate was prepared as a regular sphere with uniform size and cross stacked layers.The maximum apparent specific volume of basic magnesium carbonate reached to 10.54 mL/g.