Abstract: In this paper,by using the method of the relativistic theory,the expressions of the reflection and transmission coefficients of electromagnetic waves for a lossy plasma moving parallel to the interface are derived.It is shown that the reflected and transmitted fields are dependent on the velocity of the moving plasma if the collision are taken into account.If the collision is negligible,the result is identical with one derived by Yeh,C..In normal incident case,contrary to oblique incidence the reflected and transmitted fields are independent on the velocity of the moving plasma.