Abstract: The growth rate method was used to determine the antifungal activity of 7−hydroxycoumarin against 5 kinds of plant pathogens. Fusarium oxysporum was used as an indicator to determine the stability of the antifungal activity of 7−hydroxycoumarin under different conditions. The results showed that 7−hydroxycoumarin showed different degrees of inhibitory effect on 5 pathogens, especially on F. oxysporum. When the concentration was 1.6 mg/mL, the inhibition rate of F. oxysporum was 93.66%. The antifungal activity of 7−hydroxycoumarin was stable after treatment with light, oxidant and reducing agent, and significantly enhanced under acidic condition, but decreased under alkaline condition; after Ca²⁺ treatment, the antifungal activity of 7−hydroxycoumarin was stable; after Co²⁺ and Ni²⁺ treatment, the inhibitory effect reached 100%, and the antifungal effect was significantly enhanced after Mn²⁺ treatment; after K ⁺ treatment, the antifungal activity was inhibited.