An effective method capable of measuring the topological charges of optical vortex beams by using a generalized ring Pearcey (GRP) phase is proposed theoretically and demonstrated experimentally in this paper. The number and orientation of fringes in the diffraction patterns respectively reveal the modulus and sign of topological charges. One can also tell the sign by observing the rotation of fringes during propagation. Moreover, the measurement of high-order topological charges is shown to be significantly affected by the elliptical parameter in the GRP phase. Finally, the physical principle of these measurements is unveiled by applying the stationary phase approach. This work offers an alternative way of evaluating the photonic topological charges in vortex beams.