The invention provides a method for using pineapple peel and slag to prepare high activity dried yeast and ferment feed. The technique has the implementing steps of: crushing pineapple peel, extruding juice, separating pineapple peel juice and slag, adding the substances of molasses, ammonium sulfate and the like into pineapple peel juice, adding saccharomyces cerevisiae or candida utilis strain for liquid fermentation, carrying out separation on the yeast thallus after the fermentation is completed, drying under low temperature and obtaining active dried yeast which can be used as additives of food or feed. In addition, aspergillus niger, aspergillus oryzae, lactobacillus plantarum and complex enzyme are added into the separated pineapple slag for fermentation, and the fermented productsare used as feed which is directly fed or dried, thus being capable of reducing feed cost. The invention not only solves the environmental pollution of processing waste, changes waste into valuables,and expands the space of the feed materials and feed additives.