We present a topological charge difference detection technique for the orbital angular momentum of vortex beams. In this technique, by utilizing two vortex beams with distinct topological charges, a periodic difference pattern is generated. The orbital angular momentum of the vortex beam to be measured can be quickly and accurately calculated by reading the number of spots in one period. Compared with traditional interference and diffraction methods which require the reception of the complete vortex beam, the topological charge difference method only requires the reception of a small amount of vortex beam to measure. This has significant advantages in the measurement of high-order and large-scale vortex beams, and has potential applications in long-distance free-space optical communication of vortex beams.