Abstract: The mixer-settler is a stage-wise extraction equipment widely used in nuclear industry. Experiment was performed in bench scale to study the transient behavior of solvent extraction process in mixer-settler from start to extraction steady-state. A mathematics arithmetic was built on the basis of actual run of mixer-settler, proposed transient→steady model, and a program was developed. Generally, all the concentration profiles obtained from program are consistent with the experimental values, which demonstrates the reality of the model and algorithm. The factors affecting extraction equilibrium in 30%TBP/dodecane extraction system were analyzed using the program. And it is found that the concentration of nitric acid is the main factor.