Preparation method of herba andrographitis extract feed additive

The invention discloses a preparation method of a herba andrographitis extract feed additive, which comprises the following steps of: collecting and cleaning a complete stool of the herba andrographitis; placing a raw material in an alcohol extract pot, adding alcohol, boiling, and reflowing the alcohol; filtering after the first alcohol extraction to obtain filtrate and filter residue, processing the filtrate in a pressure reducing concentration pot to recycle the alcohol, and continuing to concentrate the strong liquor to obtain the concentrated liquor; adding the alcohol in the filtrate for the second time, boiling, reflowing the alcohol, and filtering to obtain first filtrate and first filter residue; adding water in the filter residue, boiling, filtering the filter residue to respectively obtain second filtrate and second filter residue, and discarding the residue; mixing and concentrating the concentrated liquor, the first filtrate and the second filtrate to obtain herba andrographitis extractum; loading the extractum in a container for cold storage; and drying the extractum to obtain dry extract powder. The herba andrographitis extract feed additive has the advantages of clearing heat and detoxicating, reducing swelling and easing pain, having broad-spectrum antibiosis property and the like.