In this paper, by introducing an error estimate parameter η and analyzing the magnitude of each term of the propagation equation, the propagation equation s of amplitude and phase of x-rays can be obtained in the laser-produced plasma. It is found that the change of phase is only dependent on the electron density , and the change of amplitude is directly dependent on phase. Moreover, only if η<1, by using iterative approximation, the approximate solutions of phase and amplitude can be obtained. Finally, by computer simulation these solutions a re confirmed.