The invention discloses a cover type defoamer with a defoaming function. The cover type defoamer comprises a seal cover piece provided with a gas releasing opening and a plurality of compressed gas defoaming spray guns arranged on the seal cover piece, wherein nozzles of the compressed gas defoaming spray guns point to a reaction vessel matched with the seal cover piece. By using the cover type defoamer, an acidolysis process for preparing titanium white powder by an improved sulfuric acid method comprises the following steps of: a, uniformly mixing a titanium raw material and concentrated sulfuric acid in an acidolysis pot and adding starting water to initiate a main reaction; b, starting the compressed gas defoaming spray guns in the cover type defoamer; and c, shutting off the compressed gas defoaming spray guns after the main reaction is finished. In the cover type defoamer, foams in the reaction vessel are broken by the impact effect of compressed gas, and the foams are broken forcibly to release a large quantity of gases, so that the defoamer can be used for restraining the increase of foam volume, has a defoaming effect and is suitable for a plurality of types of acidolysisprocesses.