Abstract: A rain cluster was detected in a mesoscale experiment in East China. The formula of inverse square is used here to diagnose information concerning the domain with 20 km interval horizontal grids and 11 vertical levels. During its developing and mature phases, a meso-β scale convergence system is found throughout mid-troposphere. In the developing phase, there is a positive cell in the troposphere. Strong updrafts in middle troposphere and above in the mature phase cause precipitation while downdrfats occur in the boundary layer. The decay phase is marked with much weaker ascending flow for the whole troposphere. Besides, the weak warm core in mid-troposphere rises to tropopause where it has intensified much, tending to dissipate in the decay phase.