The invention discloses a fermentation feed as well as a preparation method and application thereof, belonging to the technical field of livestock feed preparation. The fermentation feed provided in the invention comprises sunflower disk powder, rice polishing powder, corn straw powder and a fermentation product of salsola collina, wherein the sunflower disk powder accounts for 9-14 percent of the total weight of the fermentation feed, the rice polishing powder accounts for 20-50 percent of the total weight of the fermentation feed, the corn straw powder accounts for 20-30 percent of the total weight of the fermentation feed, and the balance of the fermentation product of the salsola collina. In the fermentation feed provided in the invention, unconventional materials with low cost and obvious effect are reasonably utilized and screened from common waste, and fermentation is performed by utilizing lactobacillus brevis so that the content of nitrous acid in the salsola collina is significantly reduced. By adopting the fermentation feed provided in the invention, constipation of sows in pregnancy of 90 days to 114 days can be effectively relieved, and the survival rate and daily weight gain of piglets during lactation can be significantly improved.