Abstract: Magnetic field data of controlled source audio magnetotelluric method(CSAMT) is vulnerable to electromagnetic interference, and will lead to serious degradation of phase data quality. The affected phase data are corrected by referring to the high quality phase data of adjacent measuring points and combining the least squares fitting and interpolation method. Through forward simulation analysis, it is found that cubic polynomial interpolation is effective, not only can restore the variation characteristics of phase curve more accurately, but also involve the corrected phase data in the inversion calculation, so that the inversion results are more accurate and reliable. The method is applied to the detection of water-accumulating area of goaf in a coal mine in Shanxi Province. The detection results accurately reflect the scope of the known wa-ter-accumulating area of goaf.