The invention discloses a pennisetum purpureum pig feed and a preparation method thereof. The formula comprises 63-65% of pennisetum purpureum, 8-13% of corn flour, 3-5% of brown sugar, 3-5% of strains, 5-8% of broad beans, 5-8% of soybean cakes, 5-8% of distiller's grains and 6-9% of fish meal. The preparation method comprises the following steps: step 1, raw material selection; step 2, raw material pretreatment; step 3, raw material stirring; step 4, sub-packaging and packaging; step 5, sealing and fermentation; and step 6, checking and storing. The pig feed completely replaces wheat bran, and does not contain the wheat bran component so as to avoid the problem that the wheat bran is easy to generate aflatoxin in the storage process, and to prevent the pig feed from containing aflatoxin,so that pigs fed with the pig feed are not easy to get sick or die. The feed can increase intestinal flora of pigs, improve digestive absorption, increase gastrointestinal motility, reduce ammonia concentration of pig house, and reduce probability of pig illness or death. The production cost of the pig feed is reduced by 8-10%, and the production benefit is greatly improved.