Objective To evaluate the sulfide stress corrosion cracking (SSCC) behavior of 90SS and 90SS-3Cr tube steels in H2S/ CO2 environment, and determine the fracture mechanism. Methods The SSCC behavior and fracture morphologies of 90SS and 90SS-3Cr tube steels in H2S/ CO2 environment were investigated by using four point bend test (FPB), slow strain rate test (SSRT), microstructure and scanning electron microscope (SEM) analysis. Results For 90SS-3Cr, more non-metallic inclusions appeared in the microscopic structure. After the FPB test for 720 hours, there were neither macroscopic nor microcosmic cracks on the surfaces of 90SS and 90SS-3Cr specimens, which meant that they possessed a favorable SSCC resistance. However, the SSRT tests indicated that as the concentration of H2S increased from 0 mol/ L to 6 mol/ L, the elongation, the reduction of cross section and the fracture time of 90SS-3Cr steel decreased by 71. 6% , 69. 6% and 61. 4% , which were much higher than that of 2. 9% , 52. 5% and 10. 3% of 90SS steel respectively. The fracture morphology analysis showed that the fracture of 90SS-3Cr steel transformed from ductile fracture into brittle fracture at lower H2S concentrations. Conclusion The SSCC resistance of both 90SS and 90SS-3Cr tube steels decreased with the rising of H2S concentration. 90SS-3Cr specimens were more prone to fracture than 90SS steel.