Abstract: A preparation technology of MgO powder used in special silicon steel from hydromagnesite mineral has been developed. The preparation technology includes the following steps: (1) calcining the hydromagnesite at 700-750℃ for 1.5-2 h; (2) hydrating the calcined hydromagnesite to be slurry containing the solid-liquid ratio of 15-20 g·L^-1; (3) acquiring Mg(HCO₃)₂ solution by carbonating the slurry, the carbonation temperature, CO₂ pressure, and end point PH value of carbonation are less than 40℃, 0.4-0.6 MPa, and 7 respectively during the carbonation process; (4) preparing precipitated basic magnesium carbonate by thermally decomposing the Mg(HCO₃)₂ solution at 90-100℃; (5) obtaining the MgO product by calcining the precipitated basic magnesium carbonate at 850-950℃ for 30-60 min, and adopting flowing nitrogen during the cooling process. By using this technology, more than 80wt% magnesium in hydromagnesite mineral can be extracted, and high-performance MgO products used in special silicon steel can be obtained.