The invention relates to a feed additive capable of improving the reproductive capacity of lactating sows and a preparation method and applications thereof, and belongs to the technical field of sow breeding. The feed additive comprises enteromorpha prolifera, pyrroloquinoline quinone, laminaria japonica, motherwort, cowherb seed, malt, brown sugar, licorice root, purslane, radix bupleuri, and compound amino acid. The preparation method comprises the following steps: mixing laminaria japonica, motherwort, cowherb seed, malt, brown sugar, licorice root, purslane, and radix bupleuri, then carrying out decoction and concentration, and finally mixing the concentrate with enteromorpha prolifera, pyrroloquinoline quinone, and compound amino acid. The preparation method is simple and has a low cost and good controllability. The feed additive can effectively improve the immunity of lactating sows and increase the lactation amount. Moreover, the feed additive is made of green raw materials and is safe and environmentally friendly. The feed additive is applied to the lactating sow feeds, sows can pass the nutrients to piglets, the health state of piglets is improved, the growth of piglets is promoted, and the economic benefit is increased.