To determine the studying region of China Testing Center of the Collaboratory for the Study of Earthquake Predictability （CSEP）, we adopted the Entire-Magnitude-Range （EMR） method to study the spatial distribution of minimum magnitude of completeness （Mc） in the North-South Trending Seismic Belt （NSTSB） during the period from October 1, 2008 to May 31, 2011. Also bootstrap testing was performed to estimate the uncertainty of Mc, i. e. 8Mc. The results show that Mc （EMR） = 1.6 ± 0. 03 for the whole region. From the spatial distributions of Mc we find that Mc is in the range of Mu 1.3 ±2.0 for most regions. Specifically, the spatial distribution of Mc is consistent with the distribution of stations indicating high monitoring level in the southern part and low monitoring level in the northern part. Events located with less than three stations have great influence on Me. Moreover, the uncertainty of minimum magnitude of completeness 6Mc ranges from 0. 07 to 0.22. The spatial distribution of 6Mc agrees with the seismic rate. The shorter time span may cause larger 6Mc
