The invention discloses compound premixed feed for a pregnant sow. The compound premixed feed is prepared from, by weight, 5%-10% of salt, 10%-18% of mountain flour, 10%-15% of calcium hydrophosphate, 2%-5% of L-lysine hydrochloride, 0.2%-1.5% of L-threonine, 0.8%-2% of choline chloride, 2%-6% of compound acidifier, 0.3%-0.8% of xylooligosaccharide, 1%-10% of 1% premix and the balance carriers. The compound acidifier is a coated acidifier and is prepared from lactic acid, citric acid, malic acid, fumaric acid and phosphoric acid according to the weight ratio being (5-7):(2.5-3.5):(1-2):(1.5-2.5):(1-1.5). The invention further discloses a preparation method and application of the compound premix feed. Constipation of the pregnant sow can be effectively relieved, sow faeces can be improved, and then the piglet growth speed and breeding benefits are increased. Compared with the prior art, the advantages of being free of any toxic and side effects and low in cost are achieved.