We selected the 103 M_L ≥ 2.5 earthquake waveform data on the Meng-Ning border during 2009~2015 recorded by the Inner Mongolia Digital Seismic Networks and used the simplex method Hyposat method,double difference location method,and deterministic method(PTD)for the determination of focal depth,and compared the results. The CAP moment tensor inversion method is used to determine the focal depths of the Alashan Left Flag 5.8 and 4.2 earthquakes. Finally with the deterministic method(PTD)and the double difference location method of the Meng-Ning border area we find that the focal depth results fit better with the tectonic characteristics of the border area while those with the simplex method and the Hyposat method do not. The average depth of he Meng-Ning border seismic tectonic zone is 13.32±8km.