Abstract　 　　
Since its discovery in 1997, the afterglow emission of a gamma-ray burst (GRB) has been believed to be synchrotron radiation from a relativistic blast wave. The blast wave consists of two shock waves: a forward shock (FS) wave sweeping up the ambient medium and a reverse shock (RS) wave propagating through the ejecta. A standard picture of the afterglow theory views the RS as short-lived while assuming a constant Lorentz factor for the ejected outflows. The blast wave then enters a self-similar stage where the FS dynamics is described by the Blandford-McKee solution. However, the RS is in fact believed to be long-lived as a consequence of a stratification expected on the ejecta Lorentz factors. The existence of a long-lived RS makes the FS dynamics to deviate from the Blandford-McKee solution. Recent theoretical developments made on the dynamics of such a blast wave with a long-lived RS will be presented. The FS and RS afterglow light curves will also be presented for numerical models with various ejecta stratifications and be compared with observations.