Incoherent signal subspace method (ISM) is ineffective to deal with direction of arrival (DOA) of coherent wideband signals. Although modified methods were proposed to solve this drawback, such as ISM based on modified MUSIC (MMUSIC-ISM), its performance will seriously deteriorate when the signal-to-noise ratio (SNR) is low. This paper proposes a method to construct the covariance matrix, namely denoised modified ISM (DMISM), which attempts to effectively reduce the influence of stationary white Gaussian noise. Numerical experiments affirm that DMISM outperforms MMUSIC-ISM.