Abstract: This paper presents a method of adaptive operating frequency selection for sky-wave Over-The-Horizon Radar (OTHR) with 2-D array by predicting Signal-to-Noise Ratio (SNR) of paths to the area of interest. With the elevation resolution of 2-D array, this method overcomes the incapability of separating multipath/multimode signals for OTHR with 1-D array. For frequency selecting, firstly, sounding equipments and 2-D array record the backscattering data, environment data and ionosphere state data. Propagation paths to the area of interest are deduced for available frequencies based on the ionosphere model and state. 2-D adaptive digital beam forming is employed to suppress interferences and predict the power of echoes. Finally, the paths SNR is calculated and the frequency of the maximum SNR is selected as the optimal operating frequency.