The invention belongs to the technical field of animal husbandry propagation, and particularly discloses a diluent used for boar semen and a preparation method thereof. The diluent used for boar semenis prepared from 2.85-3.15% of one-molecule crystal water glucose, 0.4465-0.4935% of one-molecule crystal water citric acid, 1.2635-1.3965% of two-molecule crystal water sodium citrate, 0.02375-0.02625% of povidone-iodine, and the balance of water for injection to 100%. The preparation method comprises the following steps: taking glucose, citric acid and sodium citrate of formula amount and sequentially dissolving in the water for injection, adding 0.25% of activated carbon for needle of preparation amount, boiling for 15min, filtering to remove carbon, and then adding povidone-iodine of formula amount for dissolving, adding the water for injection to 100%, uniformly stirring, and after pH and content are tested to be qualified, filtering, potting, and sterilizing at 105-108 DEG C for 30min by hot pressing, thus obtaining the diluent used for boar semen. The invention provides a boar semen diluent product which has a killing effect for bacteria, virus, fungus, protozoa and spore for swine artificial insemination, can effective avoid the risk of infection caused by artificial insemination, and is remarkable in practical effect and economical benefit.