Abstract: Based on the distributing characteristic of the stations and the structure in Midwestern inner Mongolia,according to the definition of the apparent stress,by using 129 earthquake waveform datum of 12 stations in middle and western inner Mongolia magnitude ranged from M_L2.5 to M_L4.5,the apparent stress in Midwestern inner Mongolia is calculated.The result shows that the average apparent stress in middle inner Mongolia and western inner Mongolia are almost similar,which basically reflects the background apparent stress level in Midwestern inner Mongolia.The temporal and spatial distribution of the apparent stress in Midwestern inner Mongolia reminds that great attention needs to be paid to earthquake potential in this area.