The invention belongs to the technical field of inorganic functional materials, and particularly relates to an Ag/dopamine/g-C3N4 visible light catalyzed bactericidal agent. An Ag/dopamine/g-C3N4 novel composite material is prepared by adopting g-C3N4 as a template and silver nitrate as a precursor and by using sodium borohydride through a reduction reaction in an ice-water bath; a novel compoundhas excellent antibacterial and bactericidal performance; moreover, the g-C3N4 and dopamine are both biocompatible materials, and per se have no toxicity to a cell. The dopamine can form a polydopamine layer with ultrahigh adhesiveness on the surface of an inorganic material through self oxidation polymerization; a catechol group in the molecule of polydopamine has certain reducibility, and can beused for reducing the ions of noble metals such as gold, sliver and the like into simple substances. Meanwhile, the metal nanoparticle and the inorganic material can generate covalent and non-covalent interaction through catechol and amino functional groups on the polydopamine; the noble metal nanoparticle can be strongly attached to the surface of a g-C3N4 material.