The present invention discloses a method for increasing the fucoxanthin content of Phaeodactylum tricornutum by using ammonium ceric sulfate. The method comprises: mixing sterilized seawater and an MAD mother liquor to obtain a nutrition liquid, adding a Phaeodactylum tricornutum mother liquor to the nutrition liquid to culture, culturing for 2 days, adding ammonium ceric sulfate, continuously culturing for 6 days, collecting the algae liquid, carrying out centrifugal separation, removing the supernatant, collecting the algae, carrying out a freeze-drying treatment on the algae for 2 days, grinding for spare, dissolving the grinded algae with dehydrated alcohol, standing for 1 h at a temperature of 4 DEG C, and centrifugating for 10 min at a temperature of 4 DEG C at a speed of 13000 rpm to obtain the supernatant. According to the present invention, the operations are simple and convenient, the cost is low, the production cycle is short, and the method is suitable for batch production and industrial production.