Abstract: The passive radar faces a significant problem in multipath clutter, and the Batch version of the Extensive Cancellation Algorithm (ECA-B) is an efficient method for clutter mitigation. However, the clutter and target echoes, whose delays are included in the cancelled range area, are modulated due to the block batch processing in the algorithm, and it results in the clutter residues and false target emergences. The modulation mechanism of ECA-B is analyzed and the corresponding compensation method is proposed in this paper. The basic principle of the method is to compensate the clutter modulation by carrier frequency offset fine estimation and then avoid the target modulation by selecting the block number properly or compensate the target modulation by estimating zero frequency components of every block signal in the modulated range cell. The simulation and real-life data results confirm the correctness of the analysis on the modulation mechanism and the validity of the proposed method, which improves the algorithm performance.