Abstract: The cross-sectional distribution characteristics of the phase interface parameters (void fraction, phase interface concentration, bubble size, etc.) of bubbly flow in helical tubes with different helical diameters were studied. The measurement accuracy of double-sensor conductivity probe was calibrated by imaging method, and then the quantitative distribution profiles of void fraction, phase interface concentration and number frequency of bubbles in helical tubes were obtained. In order to describe quantitatively the distribution characteristics of phase interface parameters, the cross-sectional average parameters, phase interface dispersion coefficient and bubble average aggregation coordinates were defined by statistical methods to characterize the distribution characteristics. The experimental results show that, with the increase of the rotating diameter of the pipe, the average void fraction of the bubble section decreases, the distribution range decreases, the average locations of aggregation move to the topside and the outside, and the overall bubble size decreases.