The invention discloses microalgae whole cell powder for making mammals produce DHA milk in high yield. The microalgae whole cell powder is prepared from raw materials of microalgae DHA cell pulp, an emulsifying agent, an antioxidant, a filler, a packing material, a dispersing agent and water. The preparation method comprises the following steps of: preparing the microalgae DHA cell pulp, and preparing an aqueous phase and a pulp phase; and mixing, emulsifying, homogenizing, spraying and premixing the aqueous phase and the pulp phase, and pelletizing to prepare the microalgae whole cell powder. The microalgae whole cell powder keeps the completeness thereof, is more easily absorbed by the mammals, and effectively keeps DHA components in the milk. Therefore, the DHA content of the finally secreted milk is much higher than that of common milk, the intake demands of all kinds of people on the DHA are met, the property is stable, and the biological functions of the DHA are fully exerted.