The beam splitter is an optical element that divides a beam of light into two or more beams. It is an essential component in many optical experiments. X-ray has the characteristics of short wavelength and strong penetration ability, making it hard to apply optical elements in the visible-light region. Therefore, it is necessary to develop optical elements suitable for X-rays. The atomic layer spacing of the perfect crystal is the same order of magnitude as the X-ray wavelength, so the crystal diffraction effect can be used to achieve the X-ray modulation. This paper analyzes the beam splitting characteristics of Laue crystal based on X-ray diffraction dynamics and simulates the influence of crystal absorption and incident light angular divergence on the rocking curves of transmission and diffraction. The modulation of the Laue diffraction beam-splitting ratio to the crystal diffraction in-plane angle and crystal thickness is presented quantitatively. The results show that the kinematical theory of X-ray diffraction is not enough to analyze the beam splitting characteristics of the crystal. It is necessary to consider the interaction between the wave fields in the crystal and use the pendellosung effect in the dynamical theory of X-ray diffraction to explain the change of the crystal beam-splitting ratio quantitatively. The influences of angular divergence and crystal absorption are considered in the simulation. The angular divergence broadens the bandwidth of the diffraction, thereby reducing diffraction intensity. Crystal absorption causes asymmetry and peak shift of the transmission curve and affects the intensity of diffraction and transmission beam. The experimental results show that the non-dispersive (%2Bn,-n) configuration can effectively eliminate the influence of angle divergence. The beam-splitting ratio can be adjusted in a small range (±2%) by changing the in-plane angle and adjusted in a wide range (±75%) by changing the crystal thickness, realizing the quantitative modulation of the intensity of transmission and diffraction beam.