Abstract:In this paper, the chemical analysis and comparison of Carbon and Sulphur and the results of the nail test at 1/4,1/2 and 3/4 of the width direction of slab are presented, It was found that the solidification terminal of 400mm ultra-thick slab was “W” solidification mode. The influence of Fs, which is the important parameters of dynamic soft reduction in Secondary Control Model, on central segregation control is analyzed, Then the conclusion is that the central solid rate Fs is replaced by the solid rate F1/4 in 1/4 of the slab width is beneficial to improve the center segregation of ultra-thick slab.