The invention provides an extractive containing total meroterpenoid of psidium guajave dialdehyde, and a preparation method and application thereof. The preparation method comprises the following steps of: (1), removing impurities from psidium guajave leaves, shearing the psidium guajave leaves, and refluxing and extracting for 1-4 times by using ethanol; and mixing extracted solutions, filtering, decompressing and concentrating to obtain a concentrated solution of the psidium guajave leaves; (2), enabling the concentrated solution to flow through a macro-porous adsorption resin chromatographic column, and eluting by using water at first, then, eluting by using low-concentration ethanol with the volume concentration of 5-20%, and finally, eluting by using high-concentration ethanol with the volume concentration of 40-100%, and collecting a high-concentration ethanol eluant; and (3), decompressing, concentrating and drying the collected eluant so as to obtain the extractive containing the total meroterpenoid of psidium guajave dialdehyde. The method disclosed by the invention is simple in preparation process; the content of the extractive can be up to 30-80%; compared with extraction by directly using an organic solvent, the yield and the content are higher; the process is also more economic and environment-friendly; and the extractive disclosed by the invention can be used for preparing medicines and health-care products for preventing and curing type II diabetes, anti-tumor microorganisms and anti-viral microorganisms.