The orbital angular momentum (OAM) of beams has important applications in various fields such as large-capacity data transmission, imaging, and quantum information. So the precise measurement of the OAM spectrum is critical. Here, we present a direct and efficient method for measuring the OAM spectrum in a scattering medium using a Faraday atomic filter. Experimental results show that the Faraday atomic filter offers significant advantages in accurately identifying OAM under scattering media when compared to the results in the filterless device and the polarizer. Our work presents a novel, to the best of our knowledge, approach to precisely measure the OAM spectrum of vortex beams in complex scattering environments and will contribute to the advancement of various applications, including optical communications, lidar, and others.