The invention relates to a method for preparing arachidonic acid (ARA) by utilizing Mortierella alpine mycelia, comprising the following steps: first carrying out deep culture on the inoculation amount of the Mortierella alpine in a constant temperature shaker; transferring and inoculating the Mortierella alpine into a container with fermentation media, obtaining fermented liquor after culturing;filtering the fermented liquor, collecting mould organisms, washing, drying and grinding the collected mould organisms, extracting or pressing the mould organisms with a nonpolar solvent, harvesting oil and fat and further processing the harvested oil and fat to obtain the target product, wherein, parts of commonly used nitrogen sources of growth media or/and fermentation media are substituted byfungal meal of Mortierella alpine and the substitution ratio of the nitrogen sources in the fungal meal of Mortierella alpine is 10-90 by mass. The residual solid matter after extracting the mould organisms with the nonpolar solvent is the recyclable fungal meal of Mortierella alpine. The wastes generated in the process of producing the ARA by utilizing the Mortierella alpine by fermentation can be recycled, thus avoiding discharge of the environmental pollutants.