The invention discloses a co-production fermentation method for astaxanthin and mannan and application of the astaxanthin and the mannan. The co-production fermentation method for the astaxanthin andthe mannan comprises: mutagenesis, preparation of protoplast, genome rearrangement, obtainment of the astaxanthin and extraction of the mannan. The astaxanthin is applied as an antioxidant additive infeeds, food and cosmetics; and the mannan can be applied in adhesives, fixatives, feed additives, cosmetic additives, embedding materials in wastewater treatment, dust preventives, chromatographic packing materials and food preservation. The beneficial effects are as follows: high-yield phaffia rhodozyma strains are obtained by a dual induction method, a strain for the high yield of the astaxanthin is screened out by a genome rearrangement and cell fusion method, so that a genetically stable phaffia rhodozyma strain is obtained, and the astaxanthin and the mannan are obtained by co-productionfermentation; the application ranges of the astaxanthin and the mannan are wide, and economic value is high.