Abstract: Fusarium oxysporum f.sp.lycopersici Fol4287 was used as the research material to explore the effects of environmental pH on the growth and infection characteristics.And tomato ‘Jimei 008’ was used as the research material, the response differences of tomato to Fol4287 stress under acidic, alkaline and neutral environmental conditions were studied by laboratory hydroponic culture and isolated leaf infection, in order to provide reference for inhibiting the occurrence of tomato Fusarium wilt by adjusting soil pH in production practice.The results showed that the optimum pH for growth and sporulation of Fol4287 was 5.0 and 9.0-11.0,respectively.The MDA content, relative conductivity, superoxide dismutase（SOD） and peroxidase（POD） activities of tomato seedlings in alkaline environment were higher than those in acidic and neutral environment, but the effect of Fol4287 was relatively weak.The damage of Fol4287 to tomato seedlings was aggravated under acidic environment.The increase of MDA content, relative conductivity, SOD and POD activities were 55.01%,67.01%,105.07% and 142.81% respectively, which were greater than those in neutral environment（19.06%,21.54%,49.81% and 70.62%）.The incidence rate of tomato seedlings in acidic environment was higher than that in neutral and alkaline environments.In conclusion, acidic environment enhanced pathogenicity of Fol4287,while alkaline environment can inhibit Fol4287 from infecting tomato seedlings although it can inhibit the normal growth of tomato seedlings.