Abstract: [Objective] Cotton Rhizoctoniosis and red rot disease are two main seedling diseases in Xinjiang cotton area.In order to obtain a strong pathogenic strain,this project aims to screen resistant varieties and disease control agents against the two diseases.[Method]In this project,30 Rhizoctonia solani and 30 Fusarium moniliforme isolated from cotton fields in south of Tianshan Mountains were used to conduct the comparative study on the pathogenicity of the susceptible cultivars(Jimian 11)after artificial inoculation.[Result]The comparison results showed that: There were significant differences in pathogenicity among the two pathogens strains;There were 8 strong pathogenic strains among the 30 Rhizoctonia solani strains,accounting for 26.7;of the total;There were 6 strong pathogenic strains among the 30 Fusarium moniliforme strains,accounting for 20;of the total;The pathogenicity of Rhizoctonia solani was significantly higher than that of Fusarium moniliforme among the two pathogenic strains;There were significant differences in pathogenicity with the strains derived from different areas in the two pathogens;In the four cotton areas of southern Xinjiang,a strain pathogenic force derived from Bazhou cotton area was relatively virulent,and virulence strain derived from Kezhou cotton areas was relatively weak;There were significant differences in pathogenicity among different strains of the same pathogen in the same area.[Conclusion]The pathogenicity of Rhizoctonia solani is significantly higher than Fusarium moniliforme in the cotton belt in the south of Tianshan Mountains and there are significant differences in pathogenicity among the two pathogens and various source strains derived from different areas.