An accurate direction-of-arrival (DOA) estimation algorithm is proposed with a uniform linear array (ULA) when coherent and uncorrelated signals coexist. By selecting the rank from the covariance matrix of array output, we first reconstruct a Toeplitz matrix so as to achieve the objective of decorrelation similar to reference [2]. And then we proposed a spectrum of improved MUSIC (named as SI-MUSIC) method to achieve a super-resolution angular estimation. Moreover, the angular resolution of the I-MUSIC method can be adjust according to the practical requirement. Simulation results demonstrate the effectiveness and performance of the proposed algorithm.