The invention provides a porcine and respiratory syndrome virus diluent and a preparation method thereof and belongs to the technical field of veterinary biological products. Every 1000 ml phosphate buffer of the diluent is prepared from, by weight, 10-30 g of amino acid combination, 10-30 g of compound traditional Chinese medicine polysaccharides and 10-30 g of liposome, wherein the amino acid combination comprises folic acid, riboflavin sodium phosphate, dexpanthenol and ascorbic acid, and the compound traditional Chinese medicine polysaccharides are extracted from pubescent angelica roots, Cymbopogon distans (Nees)A. Camus, chastetree fruit, butterflybush flowers, radix scrophulariae and red peony roots. The diluent has the advantages that after virus inoculation, cell growth can be promoted, and normal growth of cells can be maintained; viruses can infect the cells more easily after processing, and the probability that the viruses infect the cells is greatly increased; virus titer can be greatly increased in the same culture time, and virus content is increased by 10-100 times.