The invention discloses a compound feed for preventing sow constipation during gestation and a preparation method thereof, and belongs to the technical field of animal nutrition. The compound feed comprises the following components: corn, bran, soybean meal, beet pulp, apple pomace, soybean oil, calcium hydrophosphate, stone powder, lysine, methionine, threonine, sodium chloride, sodium sulfate, sodium bicarbonate, choline chloride, citric acid, a compound organic trace element premix, a compound vitamin premix, a compound enzyme preparation, a compound microecological preparation, an antioxidant and a mildew preventive. The added bran is a byproduct of wheat processing flour, the protein content of the bran is high and is 12.7%-29.5%, the content of B vitamins is high, the content of crude fibers and sulfate is high, and the bran has the effect of slightly causing diarrhea. The wheat bran is a good feed for sows, can adjust daily ration energy concentration and promote digestion, enables sows and fetuses in the middle and later periods of pregnancy to gain weight quickly, compresses intestinal tracts, causes constipation of pigs more easily, is fed with the wheat bran with a laxative effect, and can smooth the intestinal tracts and avoid abortion of the fetuses caused by constipation.