The present invention relates to a method for preparing a flavored milk soda using a liquid milk product produced animals, which may be cow milk or goat milk, and a passivation method for reducing coagulated agglomerates thereof. A method for preparing a flavored milk soda, especially a direct carbon dioxide pressurization method, which comprises the following steps: (A) opening a sealed container that can be filled with carbon dioxide in a sealed state； (B) mixing an animal-produced milk, a flavoring material and optionally water to form a flavored milk product which is filled into the sealed container； (C) closing and sealing the sealed container； (D) passivation may be carried out before casein comes in contact with acidic substances to reduce the amount of coagulated casein when considering the fact that casein in the animal-produced milk product is prone to coagulate and agglomerate into casein clusters； (E) directly filling carbon dioxide into the flavored milk in the sealed container or shaking it in such a manner that carbon dioxide is dissolved into the flavored milk and carbonizes it into a flavored milk soda； in addition to mixing the animal-produced milk product and the flavoring material, water can be added as a component, the total weight of the combination is 100 parts by weight, in which the animal-produced milk product is 2-99.99999 parts by weight, water is 0-97.99999 parts by weight, and the flavoring material is 0.00001-98 parts by weight. In case it is a method for preparing soda water by mixing carbonated water, the following steps are included: (A) opening a sealed container that can be filled with carbon dioxide in a sealed state； (B) filling water into the sealed container； (C) closing and sealing the sealed container； (D) directly filling carbon dioxide into the water in the sealed container or shaking it in such a manner that carbon dioxide is dissolved into the water and carbonizes it into carbonated water； (D) passivation may be carried
