The invention provides a diffracted wave separation method and device. The method comprises the following steps of: determining frequency space seismic data and an initial Hankel block matrix of the frequency space seismic data; carrying out Frobenius calculation on the frequency space seismic data, constructing a low-rank optimization model, acquiring an original decomposition result of original seismic data, and then determining a singular matrix, a singular value and a singular value matrix of the frequency space seismic data; determining a singular value weight matrix based on the singular matrix, the singular value and the singular value matrix by adopting a Frobenius norm least square optimization algorithm; and according to the singular matrix, the singular value, the original decomposition result and the singular value weight matrix, reconstructing the initial Hankel block matrix, and determining separated diffracted wave data. According to the diffracted wave separation method and device, adaptive calculation of a singular value weight factor is considered, a constant rank selection strategy in a traditional method is avoided, the robustness and adaptability of an algorithm are enhanced, and a diffracted wave field of high-quality separation can be obtained.