The invention provides a fattening feed for boars and a preparation method of the fattening feed, and relates to the technical field of feeds. The pig feed is prepared from corn flour, fish bone meal, maltodextrin, rapeseed dregs, breadcrumbs, dried housefly larvae powder, sesame powder, vitamin, green grass powder, yam, nutritional health wine, fructus amomi, inula flowers, dark plums, astragalus membranaceus, white atractylodes rhizome, edible salt and a proper amount of water. By the combination of concentrated feeding stuff, the smashed yam, the green grass powder, the nutritional health wine and a nutritional solution, the formula of the pig feed provides nutritional components required by growth and development for the growth of pigs, so that the demand of the pigs for nutrition is guaranteed, and the feed palatability is high; the appetite of the pigs can be stimulated, the ability of the pigs for digesting the feed is promoted, and the feed utilization rate is increased; besides, the feed contains alcohol; after the boars eat the feed, the sleeping time is prolonged, quick fattening is promoted, the period for slaughtering of the pigs is shortened, and the economical benefit is increased; and as the raw materials are environmental-friendly and are safe, the fattening feed is worthy of being popularized.