Electron acceleration by a propagating short ultra-intense laser pulse in a low-density plasma has been investigated. Electrons have the maximum energy when meeting the peak of the laser pulse. If a propagating laser pulse is abruptly stopped by a solid target, the highly energetic electrons will continue to move forward inertially and escape from the laser field. The envelope of the laser pulse is taken into account and there is an optimal position between the electron and the solid target. The
