Process for preparing high-purity dehydrated andrographolide

The invention discloses a preparing method of high-purity dehydrated andrographolide, which comprises the following steps: (1) using alcohol to immerse andrographolide; filtering; extracting medical slag; (2) soaking the medical slag in the step 1 for 24h through alcohol; fetching supernatant; (3) adorbing supernatant through large-hole adsorption resin; collecting effective eluent; condensing eluent; drying in the vacuum to obtain dried powder; (4) dissolving the dried powder through carbinol; loading in the silica gel column; eluting through composite solvent of chloroform and carbinol; collecting the effective elution; condensing; (5) crystallizing the condensate through alcohol; recrystallizing; obtaining the high-purity product.