In this article,low degree magnesite from Haicheng Liaoning is grinded and light roasted. Then pressural carbonation is treated on different conditions. The result shows that as the reaction concentration grows,carbonation rate drops in low degree. Until the former reaches 10 g/L,the falling degree becomes obvious. The faster the stirring rate,the higher the carbonation rate. When agitation rate becomes more than 400 r/min,variation is not obvious. As CO_2 pressure increases,carbonation rate grows. And when pressure becomes higher than 0. 5 MPa,carbonation rate keeps steady on the whole. Carbonation rate increases as the reaction goes on. Optimum condition is obtained through orthogonal experiment and theoretical foundation is laid for subsequent low degree magnesite refinement.