Abstract: Notches with different types (V, U), different root curvature radii (0.10, 0.13, 0.25, 0.85 mm) and different length (0.25, 0.50, 0.75, 1.00 mm) were pre-made in tensile samples from HR3C steel tube before and after service for 50 000 h, and then the notch sensitivity of the steel tube was studied by tensile tests. The results show that the unserviced HR3C steel tube had no notch sensitivity. After service, the steel tube was embrittled, and therefore became sensitive to notches. The embrittled steel tube had higher sensitivity to the V-notch than to the U-notch, especially being sensitive to the V-notches with a relatively large angle, relatively small root curvature radii (0.10-0.25 mm) and relatively long length (0.50-1.00 mm). When the stress concentration factor was greater than 3.5, the notch sensitivity of embrittled HR3C steel tube was high.