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Hot and cold model experiments were made to find out the effect of pulverized lime injection on the reaction rate during the reduction period of refining of stainless steel melt.The reduction rate of chromium oxide and the desulfurization rate were measured by the use of a 5t test converter and an 85t top- and bottom-blown converter. The capacity coefficient for reduction of chromium oxide, which proceeds on the permanent reaction site, is proportional to e0.84, where e is the input rate of stirring energy into steel melt. Desulfurization proceeds on both of the permanent and transitory reaction sites. The capacity coefficient for desulfurization in the permanent reaction site is proportional to e0.82, while that in the transitory one is proportional to e-1/3 H (m/Wm)1.5, where H is the depth of bath and (m/Wm) is the injection rate of pulverized lime per unit weight of steel melt.In the cold model experiment with iron powder injection, gas holdup in mercury was measured by means of the electroresistivity probe technique. The upward flow velocity of the mixture of gas, liquid and solid is proportional to the cubic root of e.The effects of the operation factors such as m, H and gas flow rate, q, on the desulfurization rate were analyzed under the consideration of the two reaction sites. The ratio of desulfurization rate in the transitory site to that in the overall one increases with increases in m/Wm and H, and with a decrease in q. Moreover, the relation between q and H was calculated in the lime injection practice whose desulfurization rate was equal to that without lime injection on the basis of the experimental results.