The measurement of the topological charges of a composite vortex beam is challenging. Therefore, this study proposes a method to detect the orbital angular momentum of each sub-beam using the light intensity distribution characteristics and diffraction patterns with an elliptical aperture occluding partial azimuth. Simulation results reveal that the number of bright stripes and the direction of the tail in the intensity distribution of the composite beam represent the absolute value of the topological charge difference and the symbols of the higher order topological charge, respectively. The number of dark stripes and their distribution characteristics in the diffraction patterns reflect the size and symbol of the low-order topological charge, respectively. Thus, the proposed method can successfully detect the topological charges of composite vortex beams.