A method for treating waste gas containing inorganic acid is disclosed. The method includes the following steps: (a) forming a mixture of inorganic acidic gas and a nebulized alkaline solution wherein the nebulized alkaline solution can be produced continuously or periodically; (b) forcing the mixture to pass through an adsorbent bed; and (c) releasing the treated gas. An apparatus for treating the inorganic acid gas with the method illustrated above is also disclosed here. The method can regenerate poisoned adsorbents online, and save time, space and cost simultaneously.