[en] This paper studies the output properties of GeV electron bunches driven by ultra-intense lasers in vacuum based on the mechanism of capture and violent acceleration scenario [CAS, see e.g. J.X. Wang, et al., Phys. Rev. E 58 (1998) 6575]. We find that the output of the acceleration mechanism is a GeV electron macro-pulse which consists of many micro-pulses corresponding to the periodicity of the laser wave. The outgoing electrons can generally be divided into two groups. One spreads greatly in space and the other is a high-energy bunch with limited spread in space. Provided that the incoming electron bunch with comparable sizes as that of the laser pulse synchronously impinges on the laser pulse, the total fraction of CAS electrons can reach more than 20% of the incident electrons. These results demonstrate that the CAS is a pretty effective accelerator mechanism