Abstract: The disclosure relates to a multifunctional water-based coating and its preparation method. The coating consists of a surface-grafted flower-ball-shaped nano cuprous oxide, nano lithium silicate, a water-based acrylic emulsion, a wetting agent, a defoaming agent and a dispersing agent. The flower-ball-shaped nano cuprous oxide is etched by introducing a bacterial liquid and is subjected to surface modification by using a silane coupling agent, titanium dioxide, silicon dioxide, etc., so as to improve the performances of the coating layer such as fouling resistance, strength, dispersibility, ageing resistance and insolation resistance. The coating of the disclosure has multiple functions, a wide application range and a long service life, and can be used for surface protection of marine facilities, coastal buildings and coastal steel structures. The materials used are cheap and easy to obtain, have no pollution to the environment, and are suitable for large-scale production.