With the rapid development of Ultr-afast laser technology,the generation of Terahertz electromagnetic wave(THz wave) by ultra-fast opto-electronic technology were more and more noted.The electromagnetic wave with range 0.5 ~ 5THz has a significance in the spectrum which is obtained from the use of ultrafast laser technology indirectly.Currently,there are two user-friendly ways to generate pulsed THz radiation:one is through rapidly modulating the photocurrent of the semiconductor antenna; the other is to use a femtosecond pulsed laser irradiation photoconductive switch.But high-power terahertz electromagnetic wave radiant point remains to be further developed.This paper will conduct the experimental and theoretical research on the far-field characteristic of terahertz radiation for dipole antenna of the GaAs photoconductive switches with an ultrahigh electric fields triggered by the femtosecond laser pulses.