Abstract: A spatial aliasing-free direction of arrival (DOA) estimation method based on improved frequency difference (FD) technology has been proposed, which achieves sparse array element arrangement, that is, when the array element spacing is much longer than the incident signal wavelength, the DOA estimation of multiple underwater acoustic targets in the presence of gate lobe ambiguity is achieved. Firstly, the target azimuth angle search range is determined, the array signal processing model is established, and the frequency difference processing is performed between the different frequency components of the wideband signal, so as to reduce the signal frequency to meet the spatial Nyquist sampling requirements of the array with sparse array elements. Then, based on the test of orthogonality of projected subspaces, a diagonal transformation matrix is constructed, and the orthogonality of the diagonal unitary transformation matrix is used to directly perform frequency difference processing on the array manifold, so that the number of signals output by the frequency difference processing is equal to the number of input signals. Finally, the condition for the equivalence between the equivalent target orientation and the true incident signal angle in the frequency difference domain is further derived, and frequency screening is performed based on this equivalence condition, ultimately obtaining a spatial orientation spectrum result without ambiguity. The simulation results show that the root-mean-square deviation of the proposed algorithm is less than 0.1° in the signal to noise ratio range of −10−20 dB, which effectively suppresses the gate lobe and is less affected by the interference intensity. Verified by sea experiment data, the proposed algorithm can effectively estimate the target orientation and avoid spatial aliasing interference. The proposed spatial aliasing-free DOA estimation method can effectively suppress gate lobe ambiguity, improve target direction estimation accuracy, and still have good angle estimation performance under strong interference conditions.