Abstract: Heat transfer in square annular upward flow channel was studied on the supercritical water heat transfer facility at Xi’an Jiaotong University.Experimental pressure is range of 23~25 MPa,mass ve-locities of 500~1 200 kg/（m²·s）,heat fluxes of 200~800 kW/ m²,and bulk inlet temperatures of 300~400 ℃.Experiment results showed that at high mass velocity and relatively low heat flux,the heat transfer in square annular geometry with helical wire-wrapped spacer would be enhanced,whereas at low mass velocity and relatively high mass flux,the heat transfer deterioration would occur.Comparison of experiment data showed that at lower supercritical pressure,heat transfer was enhanced more impressively but the deterioration was more likely to occur while relatively higher supercritical pressure means better security.