Abstract: A comprehensive analysis is conducted to investigate the weather background, hail characteristics, radar echo evolution and three-dimensional echo structure of the hail clouds that developed in the eastern foothill of the Taihang Mountains in the afternoon of 13 June 2018. Observations of the SA Doppler weather radar in Shijiazhuang and the X-band dual polarization radar in Raoyang are used in this study. Three-dimensional (3D) gridded wind velocity (flow field) is retrieved from the radial velocity of the dual Doppler radar, and the hail cloud structure is analyzed based on the echo characteristics. The results show that the strong upper-level northerly jet caused the transverse trough to turn vertical, and the cold air behind the trough moved southward along the northerly airflow. Unstable stratification developed with cold and dry air above warm and wet air, which resulted in the hail weather near the low-level vortex and along the convergence line in the surface. The wind field retrieved from dual-Doppler radar observations shows that in the middle layer of the hail storm, there existed obvious S-shaped horizontal flow with characteristics of suspended echo. This is a typical "zero-line" structure conductive to hail formation. The existence of the "zero line" structure is confirmed by the observed 3D structure in hail storm and the diversity of its manifestation is demonstrated.