This article proposes the calculation of the probabilities of incoherent reception of signals with binary relative phase manipulation (OFM–2) in the presence of several harmonic interference. Examples of calculating the error probability per bit of receiving signals from OFM – 2 according to the presented method in the presence of several harmonic interference are shown. The obtained graphs depend on the magnitude of the signal at different values of interference and the same magnitude of the frequency shift, as well as on the frequency shift of interference at different levels of signals and interference. The results of the study using this technique allow us to calculate with high accuracy and reliable forecasting the reliability of transmitted information in radio communication channels under the influence of several harmonic interference during processing on two clock cycles. And also to predict the maximum damage to the process of transmitting information in a radio communication channel under various conditions: the coincidence of interference frequencies with the signal frequency, the offset of interference frequencies relative to the signal frequency and the spread of interference frequencies with the signal frequency.