The invention provides a preparation method of a capsule preparation (Antaituo capsule) for treating pharyngitis and infection of the upper respiratory tract and a quality detection method of the capsule. The preparation method comprises the steps of: taking 350 g of iris tectorum maxim total flavonoids, drying to make the moisture content lower than 5%, smashing into fine powder which can pass through a 60-mesh screen, adding talcum powder accounting for1-3% by weight of the fine power,mixing evenly, and loading into a number one hard capsule. Besides a check on general projects according to the pharmacopoeia general rule, in the detection method, methods for identifying the main active ingredient tectoridin are formulated, comprising spectrophotometry and thin layer chromatography; the content of the iris tectorum maxim total flavonoids is determined through the spectrophotometry to ensure that the quantity of the active ingredient is more steady, and the quality of the preparation is effectively controlled to ensure the clinical effects, thereby the safe and effective medication for people is ensured.