Abstract: In this paper, the Maxwell equations of Xray laser beam through stationary plasma was written as the equation in the form of timedependent Schr〖ＡＫo¨４〗edinger equation (TDSE), the generalized Huygens' integral was derived in terms of evolution operators from the viewpoint of quantum mechanics for the first time, and the analytical relationship of the electron density of plasma with the phase difference of the Xray through stationary plasma with gain and the same Xray through vacuum under the optical thin approximation (its diffraction effects are negligible)．