The invention discloses a method for preventing and controlling fungal diseases of cucumbers. The method comprises the steps of firstly inserting an ozone generator conduit into a container containing plant oil, introducing ozone for continuous treatment and performing saturation ozonization on the plant oil; adding a surfactant into the plant oil processed by the ozone and diluting and uniformly stirring with 10-100 times volume of water to prepare into an oil emulsion, and spraying the oil emulsion onto plant faces of cultivation soil of plants. The method for preventing fungal diseases of the cucumbers can ensure the durability of medical effect and can realize the controllability on use concentration. Experiments show that the sterilization effect of the method is not lower than the currently universal chemical fungicides such as carbendazim and procymidone, and the method has no side effects on plants, is simple and convenient to apply, and has the broad spectrum killing effect on harmful pathogenic microorganisms such as various funguses and germs beyond comparison with organic chemical pesticides.