Direction Of Arrival(DOA) estimation for wideband signal is one of the hot issues in wideband array signal processing. Aperture fill effect is an important factor to affect the estimation precision of wideband DOA when wideband signal range resolution and wideband aperture are comparable. On the basis of the linear coupling characteristic between spatial domain and frequency domain of wideband array signal, Keystone transform is adopted for decoupling. Then the decoupled data is used for DOA estimation with coherent accumulation method. The results of simulation show that the precision of DOA estimation is improved remarkably by eliminating the effect of aperture fill effect. The proposed algorithm is an effective method due to its lower computational complexity and higher DOA estimation precision.