This article deals with the saprophytic colonization of F.oxysporum on plant residues in relation to its survival in soil.Most of the plant residues,such as the straws of wheat,rice,bean,cotton,milk vetch,etc.,are easily colonized by F.oxysporum in soil under dry farming,even if those have been colonized previously by Chaetomium,Mucor,dsPergillus,Rhieoctonia,Sordatia and other soil fungi.The temperature and soil moisture adapted to saprophytic colonization ranged from 15°-30℃ and 20-80% of moisture holding capacity respectively.Fungal growth was suppressed in submerged soil due to lack of oxygen,while colonization still occurred on residues floated above the water.Propagule density of the pathogen in heavily infested soil decreased sharply under flooding condition,but it could not be entirely eliminated from flooded rice growing soil.It existed in the oxidation layer and propagated gradully as saprophytes or parasites after 1 or 2 successive cotton croppings.When fresh organic matter was added into the soil under flooding condition,the pathogen diminished with the decline of soil Eh.