Abstract: The effects of pH value and steam pressure of treating solvent on the acidity of β zeolite were investigated.The results showed that the acidity density of zeolite decreased after treating with steam.The higher the steam pressure,the lower the acidity density.When treated with basic solvent, the acidity density of the sample almost remained unchanged;while acidity density decreased with reducing pH value when treated with acidic solvent.The relative content of Bronsted acid reduced after treating with steam or acid/base solvent.Bronsted acid of zeolite surface could convert into Lewis acid in the modification process.