The kinetics of denitrogenation from liquid steel was studied by using an oxygen--nitrogen analysis system(LECO TC-436) under 1600'C~2813'C conditions. The results show that when [S]=0.005%, nitrogen removal was controlled by nitrogen transfer in liquid difFusion layer, when [S]=0.012% and 0.140%. it was controlled by both nitrogen transfer in liquid diffusion layer and the chemical reaction at the liquid-gas interface below 2250'C, and by nitrogen transfer in liquid diffusion layer under 2250'C~2813'C conditions. The activation energy Ea was 57 kJ/mol for 0.0050%[S], 95 kJ/mol for 0.012%[S], 165 kJ/mol for 0.140%[S]. The resistance of sulphur on nitrogen removal decreased with the temperature rose, and disappeared at 2630'C. Based on the results obtained. it has been answered why the nitrogen in liquid steel can be decreased rapidly by carbon-oxygen reaction under very high oxygen and sulphur content conditions during the BOF, EAF, VOD and AOD steelmaking processes.