The mesoscale characteristics of the regional rain storm over the central Shanxi Province on 26, 27 July 2001 are analyzed on the basis of GMS5 infrared imagery and some conventional observation. The results show that (1) This event is caused directly by a newly developed mesoβ scale cloud cluster. (2) There existed a Ωshaped energy field on the surface, and there was a mesoscale convergence line and an anticyclone. The mesoscale rainfall cluster formed to the north of the convergence line and the southeast side of the mesoanticyclone. The convergence area was overlapped with the high energy tongue where there was strong ascending motion, which triggered energy release, was the main dynamic mechanism of the rainstorm. (3) Mesoscale characteristics can be seen in the distribution of frontogenesis function of wet 〖WTHX〗Q〖WTBZ〗vector. The center of strong frontogenesis function lied in the southeast of mesoβ scale cloud cluster, which was the main startup mechanism of the rainstorm. There was positive correlation between the center of frontogenesis function at the lower levels and the rainfall amount with a time lag of 6 hours.