AbstractThis study compares five methods for estimating the completeness magnitude Mc threshold of earthquake catalogs through applying them to synthetic catalogs generated from 3 different models. We have found that the Median‐based analysis of the segment slope (MBASS) method is suitable for catalogs recorded by networks whose detection capability changes rapidly with magnitude and for those with spatiotemporal heterogeneity if the amount of earthquakes is large enough. The Mc by b value stability (MBS) method is optimal in dealing with catalogs recorded by networks whose detection ability improves slowly with magnitude, but it is time‐consuming. The Maximum Curvature technique (MAXC) & Goodness‐of‐fit method (GFT) underestimate Mc and need an Mc criterion. The Mc from Entire Magnitude Range (EMR) method gives a stable and moderate Mc estimation. It is recommended when the amount of events is not large and the tolerance of missing events is relatively high. This study helps us to choose the optimal Mc estimation method in practice to cope with different earthquake catalogs and points out some potential problems caused by these methods.