Experiments of steam-water two-phase flow frictional pressure drop in a vertical helical coil were carried out in the high-pressure water test loop of Xi'an Jiaotong University. The coil is made of stainless steel tube with an inner diameter of 16mm, the helix diameter measured from tube axis to tube axis is 1.3m, and helix angle of the coll is 3.65℃. The experimental conditions are: pressure p=4～18MPa, mass velocity G=400～1400kg/(m2s), inner wall heat flux q=100～700kW/m2. Based on these data, a correlation for predicting the steam-water two-phase flow frictional pressure drop was derived, it can be used for the design of steam generator of HTGR.