Abstract: When 15mg稬^-1 LaCl₃ was used to spray wintersweet three times ,it reduced the damage effect of simulated acid rain at pH 2.5. It was considered that the effect of LaCl₃ on the wintersweet was realted to following factors.(1)Raising photosynthetic rate and chlorophyll content;(2)increasing catalase activity;(3)decreasing malondialdehyde content; (4)reducing cell membrane permeability and (5)keeping stability of pH value of cell juice.