Abstract: Different concentrations of PEG were used to assess the effect on morphological characteristics and physiological indices of the prothallus of Adiantum reniforme var. sinense and Adiantum flabellulatum. By means of artificial simulated drought stress, three concentrations (0% , 15% , 30% ) of PEG were selected to study the change of cell morphology, protective enzyme activity and osmoregulatory molecules in leaves. With drought stress deepening, the prothallus became darker and grew worse; MDA content of two treatment groups (15% and 30% ) was lower than that of the control group; Pro content did not increase distinctly during the period of drought stress; SP content of two treatment groups all increased firstly and then decreased, and they were remarkably higher than that of the control group; SOD activity of three groups of Adiantum reniforme var. sinense increased first and then decreased, while two treatment groups of Adiantum flabellulatum decreased all the time; CAT activity was increasing significantly. It was concluded that SP and CAT activity could reflect the ability of drought resistance for these two ferns’prothallus. The study could also provide theoretical basis for the development and utilization of fern.