The probability property of the orbital angular momentum (OAM) distortion of the Bessel Gaussian beam propagating through the turbulence is investigated in this study. The mean and variance of the beam harmonic intensity are derived from the Rytov theory with a bias of less than 6% when compared with the data calculated by the phase-screen method. Based on these statistics, the probability density function (PDF) of the harmonic intensity fluctuation is proposed to characterize the randomness property of the beam OAM distortion, which agrees well with the result obtained from the phase-screen method. The PDF of the intensity difference between the fundamental and its adjacent crosstalk modes is derived. Furthermore, the probability of the OAM decoding error is also provided. This study not only facilitates beam OAM crosstalk characterization, but also provides the applicable condition of beam multiplexing for the beam parameter selection and the communication link design.