Abstract: Responses of 9 species of herbaceous ornamental to simulated acid rain(pH 2.0,3.0 and 3.5) in cytoplasma membrane permeability and chlorophyll content in leaves were studied.A remarkably negative correlation was found between acid rain stress and chlorophyll content.The more frequent the acid rain stress,the lower the chlorophyll content.But the extent of the variation vary with pH value.After the stress was removed,chlorophyll contents in these plants came back gradually with rates depending on sensitivity of each plant to acid rain(sensitive plantsmoderate plants>resistant plants).After the treatments of acid rain,the leave cytoplasma membrane permeability of 3 groups of plants peaked in 48 hours and then declined,showing a saddle-shaped curve throughout the experiment and following the same order,sensitive plants>moderate plants>resistant plants,in variation degree.