The control and handling of fluids is central to many applications of the lab-on-chip.This paper analyzes thebasic theory of manipulating different electrolytes and finds the two-dimensional model.Coulomb force and dielectricforce belonging to the body force of different electrolytes in the microchannel were analyzed.The force criterion atthe interface was concluded,and testified by the specific example.Three basic equations were analyzed and applied tosimulate the phenomenon.The force criterion was proved to be correct based on the simulation results.