The invention relates to an application of schisandrin B in the preparation of a diluted liquid for preserving boar semen. The invention also relates to a diluted liquid for preserving boar semen. The diluted liquid comprises glucose, sodium bicarbonate, sodium citrate, EDTA, critic acid, potassium chloride, gentamycin, and schisandrin B. The effect of the provided diluted liquid for preserving boar semen is good and reliable. The high quality semen stored at a room temperature can be provided for pig artificial insemination. After the boar semen is preserved in the diluted liquid at a temperature lower than 17 DEG C for five days, the semen activity is still above 0.6.