Abstract: In near-critical pressure region, for the purpose of investigating critical heat flux (CHF) of departure from nucleate boiling (DNB) in a vertical upward rifled tube, the experiment was conducted with the range of pressure from 18 to 21 MPa, mass flux from 500 to 1000 kg/(m²•s), inlet subcooling temperature from 3 to 5 ℃ and inner wall heat flux from 40 to 960 kW/m² in a six-head rifled tube with the size of 35 mm×5.67 mm. The inner tube wall temperature and heat transfer coefficient distribution in different operating conditions were obtained in the experiment. The effects of the operating parameters on CHF were analyzed. Meanwhile, based on the experimental data, a heat transfer correlation utilized in two-phase region and an empirical correlation used to predict the critical heat flux recorded as q_CHF were developed. Moreover, experimental q_CHF in the rifled tube was compared with predicted q_CHF in smooth tube, revealing the enhancement effect of CHF in rifled tube. The experimental results show that at near-critical pressure, DNB can occur at low vapor quality and even in subcooled region in rifled tube. The increase of pressure and the decrease of mass flux can both lead to the earlier occurrence of DNB. Meanwhile, q_CHF increases with the decrease of pressure and the increase of mass flux. In addition, in specific operating conditions, DNB and dryout can coexist at different sections of the rifled tube respectively.