The invention relates to the technical field of health-care product dosage forms and in particular to an oral cavity micro-effervescent tablet and a preparation method thereof. The oral cavity micro-effervescent tablet comprises a nutrient, sugar alcohol, an acid source, an alkali source, magnesium stearate, essence and a sweetening agent, wherein the sugar alcohol is a combination of one or moreof lactose, maltitol, sorbitol, isomaltitol, mannitol and erythritol; and the sweetening agent is a combination of one or more of sucralose, Abbas sweet, stevioside, fructose, white granulated sugar and mogroside. By adding a suitable amount of acid-base, the sweetening agent and the essence to a nutrient substance, and under the action of saliva in an oral cavity, the oral cavity micro-effervescent tablet has the advantages of micro-effervescence, good mouthfeel, and strong experience feeling. At the same time, the product is capable of solving a problem that moisture absorption of an effervescent tablet is serious in a production process or an acceleration test.