A AlAs/GaAs/AlAs/AlGaAs double-barrier superlattice grown on GaAs substrate by MBE has been studied by combining double-crystal X-ray diffraction and synchrotron radiation. This combination provides a comprehensive structural analysis. During simulated by X-ray dynamical diffraction theory, we find the intensity of satellite peaks which situated near-by the modulated wave point of one layer are very sensitive to the variation of the layer's structural parameters. Accoding to these, the accurate layer thickness can be get with an error less than 0.1nm. The modulated phenomenon is investigated by X-ray kinematical diffraction theory.