With the increase of strain, the degree of sensitization of 304 stainless steels increased and desensitization did not occur in 240h at 380°C. Although the stress relaxation appeared, the reversed transformation of strain-induced martensite was scarcely observed. Therefore, strain-induced α′-martensite could lead directly to increase of degree of sensitization. Unlike the sensitization at lower temperature, tensile pre-strain promoted desensitization in higher temperature at 575°C and 675°C. The higher the sensitization temperature was, the lower the degree of sensitization was. The higher temperature promoted reversed transformation of strain-induced α′-martensite and facilitated recovery and recrystallization of reversed transformed austenite, which resulted in decreased degree of sensitization.