Abstract: A severe hailstorm occurred in northeast of Sichuan on Apr.29, 2007.In this paper, the synoptic situation and characteristics of physical quantity field before the hailfall are analyzed by using the data of atmosphere combosite observation and grid-point field from NCEP/NCAR reanalysis.The evolution process and the structure of the hailstorm are also analyzed on the basis of a Doppler weather radar and satellite images.The results show that before hailfall, there is a warm advection at the low level, low energy level in the PBL, cold advection or a center of positive vorticity in the mid-and upper-level, strong cold vortex on the upper leve.The MCS activity occurred on the satellite cloud image over the northwest of the hailfall area.The observation of Doppler radar show that before hailfall, there are overhang echo, mesocyclone, and BWER (bounded weak echo region) with the partial features of the typical supercell storm.