The invention discloses nano silver-containing trimolybdate and a preparation method and use thereof as an antibacterial agent. The molecular formula of the silver-containing trimolybdate is (NH4)2-xAgxMo3O10, wherein x is equal to 0.58, and the silver-containing trimolybdate is a nanowire. The silver-containing trimolybdate is prepared by reacting ammonium heptamolybdate tetrahydrate with a silver salt in water. The invention also discloses the use of the silver-containing trimolybdate nanowire as the antibacterial agent. The use of the silver-containing trimolybdate nanowire as the antibacterial agent, which is disclosed by the invention, does not require grinding. The silver content in silver-containing trimolybdate is high, so the required amount for achieving the same antibacterial effect is small; meanwhile, the molybdenum compound also has an antibacterial function, oxy-acid radicals containing a positive hexavalent molybdenum element in the solution also have certain oxidability, and thus, the molybdenum element can promote the antibacterial effect of the silver ions; therefore, the nano silver-containing trimolybdate has double antibacterial effects, and the antibacterial capacity of the nano silver-containing trimolybdate is 1,000 times that of a micrometer antibacterial agent. The preparation method disclosed by the invention is simple, has low equipment condition requirements, reduces reaction time and is suitable for large-scale production.