Orbital angular momentum (OAM) with the potentially revolutionary improvement in wireless capacity has become one of the candidate technologies in the future sixth generation (6G) communications systems. However, the capacity of OAM communication system has not been fully investigated in non-ideal multipath propagation. In this paper, the channel capacity performance of an OAM-MIMO system is presented in an indoor open corridor scenario considering the complex and diverse multipath environment. Numerical results validate that the capacity of the OAM-MIMO communication system decreases with the increase of the radii of the antenna arrays and the reflection distance. Also, the capacity of OAM-MIMO system is superior to the traditional MIMO system under different propagation conditions. More generally, our results suggest fundamental parameters that can be used in OAM communication in real multipath environments.