In this paper, the beam propagation of X-rays in an inhomogeneous isotropic plasma is studied. The electron density gradient of a laser-produced plasma affects trot only the beam width but also the curvature radius of the wave front and the amptitude of the light field. A diffraction-integral-like solution is derived, in which the effect of the electron density gradient has been included. This result can explain, theoretically, the diffraction and the light deflection of X-ray propagation in an inhomogeneous plasma.