Abstract: Based on diffusion equation, the concentration of hydrogen isotopes and helium in the stainless steel film specimen aging at room temperature for two years was calculated and measured by finite diffusion method. The fracture strength was measured by tension test. The SEM and PAT were applied for the investigation of the fracture. The initiation and propagation of cracks were investigated in situ by tension in TEM at room temperature. The effect of tritium on the fracture of stainless steel was evaluated. The results show that the concentration of helium from the decay of tritium in the stainless steel aging at room temperature for two years is up to 30 ppm. The fracture strength decreases by the existence of helium and tritium. The increase of the defects makes the lifetime of positron annihilation longer. There are no helium bubbles by TEM. The tension process in TEM indicates that the tritium provokes the emission, propagation of dislocation in the cracks tip. The micro fracture process of HR-1 SS and HR-2 SS can be described that tritium cracks nucleate, blunt to microvoids and then incorporate into crazing tritium which results in the lessening or vanishing of the dislocation free zone (DFZ) for HR-2 SS.