The existence of F. oxysporum f. sp. vasinfectum in relation to the fluctuation of propagules in soil under different edaphie conditions was studied in vitro. It was shown that the ehlamydospores of this fungus were easily formed in upland field. But under vaaterlogged soil condition, formation of chlamydospores was inhibited because of the lack of oxygen and the toxicity of CO₂. The germinated chlamydospores were capable of making further propagation under well aerated soil condition. However, in submerged soils, the germlings were easily suffered from bacteriolysis in soil in a few days. As a result, propagules decreased gradually. Part of the ungerminated chlamydospores persiated. in soil for a long time under submerged soil condition. Some of them can even survive more than 160 days. It is inferred that those chlamydospores still remained in soil might be one of the most important causative agents of reinfection, and it may be the reason that this fungus can not be eliminated and the wilt disease of cotton can not be completely controlled under rice-cotton rotation.