The numerical simulation about flow and heat transfer characteristics of n-decane under supercritical pressure in the tube with round protrusions is researched in this study. The heat transfer enhancement mechanism of protuberant tube is conducted by realizable k-ε model. The average outer wall temperature of protuberant tube is reduced by approximately 60–80 K and the Nu is 45–55 greater rather than smooth structure within the operating cases. When comparing with smooth tube, the thermal performance of protuberant tube increased by 62.5%–81.4%, and the whole heat transfer performance increased by 15.6%–32.4%. The obvious heat transfer enhancement of protuberant tube is attributed to the effective destruction of thermal and flow boundary layer. Forced mixing effects of protrusions enhance flow and heat transfer further. Besides, the effects of protrusion height, pitch and circumferential number on flow and heat transfer performance are also studied. The results reveal that the increase of protrusion height and circumferential number can simultaneously rise the Nuc/Nus and fc/fs, while the increase of protrusion pitch is contrary. Among all working conditions, the protuberant tube of H = 0.5 mm, P = 4 mm and Nc = 6 obtains the largest PEC = 1.35.