The invention relates to an yttria-straw cellulose composite nanometer antibacterial material. The preparation method comprises the following steps: uniformly dispersing extracted straw cellulose into an yttria synthesis system, reacting in a high pressure reactor, performing centrifugal separation on the precipitate, drying and staying overnight so as to obtain an yttria-straw cellulose compound; performing absolute ethyl alcohol sterilization on a nanometer material, centrifuging and removing the supernatant, adding water for fully and uniformly mixing; adding yttria-straw cellulose compound materials of different concentrations into test tubes with a certain concentration of Escherichia coli and staphylococcus, and respectively shaking and culturing under light and darkness for a certain time; and analyzing the inhibition efficiency of the nanometer material on Gram negative bacteria and Gram-positive bacteria by utilizing a plate count method. The yttria-straw cellulose composite material has excellent effects of inhibiting the Gram negative bacteria and Gram-positive bacteria, particularly has extremely high efficiency of inhibiting the Gram negative bacteria, is environmentally friendly and does not cause problems such as drug tolerance of bacteria and the like.