In free space, an orbital angular momentum (OAM) beam can be affected by atmospheric turbulence, which distorts the beam’s spiral phase and degrades the signal quality after demodulation. To study the effects of different conditions of atmospheric turbulence on orthogonal frequency division multiplexing (OFDM)-OAM optical signals, a non-Kolmogorov turbulence model is used to simulate atmospheric turbulence by varying the refractive-index structure constant Cn2 and atmospheric index α. The intensity profile of a demodulated Gauss beam as well as the light intensity and bit error rate of an OFDM-16QAM signal carried by an OAM beam are tested experimentally. Variations of Cn2 and α affect the Gauss beam and the detected OFDM signal while channel coding reduces the effect of turbulence to some extent.