Single drop technique is a good method for studying mass transfer in solvent extraction because of its accurate results and simple equipment.The mass transfer coefficient of forward extraction of boric acid from salt lake brine by 2-ethyl-1，3-hexanediol in toluene was investigated.The result shows that the mass transfer coefficient increases with the increasing of temperature and initial concentrations of 2-ethyl-1，3-hexanediol in the organic phase and boric acid in aqueous phase.The model of mass transfer coefficient was established with two-film theory model by considering the modified correlation of mass transfer coefficient.The average relative error of calculated and experimental value of the model was 7.59%，which showed that the results were in good agreement with experimental values.The model can be used to design and scale boric acid extraction process by 2-ethyl-1，3-hexanediol-toluene.