A new method for description of electro-optic detection for THz radiation, using wave coupling theory of linear electro-optic effect,is presented in this paper. This method is not only useable in all optically isotropic detection crystals,bu t also usable in the situation that the probe beam propagates along the optical axis of uniaxial crystals.Also,the description method can be used for all possib le polarization directions of the probe beam and for arbitrary direction of the electric field of THz radiation.The description does not need complex coordinate transform,and the calculation is very simple.Finally,some conclusions have been drawn.