GaAs photoconductive switch illuminated by a femto-second laser has been widely used in a terabertz (THz) time domain spectroscopy system as a THz wave emission antenna. Now, all of the GaAs photoconductive switches are used in linear mode. However, when the GaAs photoconductive switch operates in an avalanche multiplication mode, the power capacity of output ultrafast electric pulse is much higher than that in a linear mode. So far, nobody has proposed the idea of generating THz waves by using the GaAs photoconductive switches in the avalanche multiplication mode. In this paper, we report the feasibility and research progress of using the GaAs photoconductive switches in the avalanche multiplication mode as the THz sources. By theoretical analysis and experimental research, some results are obtained experimentally as follows. 1) The GaAs photoconductive antenna can operate in an avalanche multiplication mode when illuminated by a femto-second laser pulse with an energy on the order of nJ. 2) The maintaining time of the avalanche multiplication mode, i.e, lock-on period, can be reduced by the quenching mode of photo-activated charge domain. These results lay the foundation for generating the high intensity THz emission by the GaAs photoconductive antenna with the avalanche multiplication mechanism.