Abstract: β-mannanase is one kind of new feed additives.Adding β-mannanase can promote the multiplication of intestinal beneficial bacteria in animals,suppresses the growth of harmful bacteria,maintain the ecological equilibrium of intestinal microorganisms,enhance the immunity and the disease resistance of animal organism,increase the digestibility of mannan in feed by poultry,decrease the chyme viscosity in the alimentary tract of poultry,enhance the digestion and absorption of nutrients in intestinal tract and reduce the environmental pollution by poultry excreta.The research progresses on β-mannanase for forage were expounded from three aspects of the source and mechanism of β-mannanase and its application in poultry feed.