A broadband solar radio type Ⅲ burst was observed on August 25,1999 at Purple Mountain Observatory with waveband of 4.5-7.5 GHz. It was also observed at Beijing Astronomical Observatory with waveband of 5.2-7.6 GHz. Therefore, it is the first common spectral event observed in China. The type Ⅲ bursts are gathered into more than 10 groups and drift in opposite directions, but the reverse drifting prevails. The largest bandwidth of type Ⅲ burst reaches ≥3 GHz and may be the broadest bandwidth of the reverse type Ⅲ burst ever observed up to the present. Some new observing characteristics of fine structures are found, for example, fiber-like, V-shaped and neck-ring-like structures. Especially, the neck-ring-like structure is probably first discovered in cm waveband and may be the evidence of twisted rope of magnetic lines.