One-dimensional pseudo-homogeneous model of an axial flow converter and one-dimensional heterogeneous model of a horizontal converter have been presented, which describe the distribution of gaseous composition, temperature and pressure along the height in the two converters, respectively. Design optimization methods of the two converters have been proposed, by which the minimum catalyst volume can be obtained to satisfy the productive capacity of 1000 tons per day, when the operating pressure is 15.0, 10.0 and 7.5 MPa, respectively.