Abstract: Based on the focal mechanism solutions above depth of 70 km around the M_W8.3 Chile earthquake on 16 September 2015 collected from GCMT, this paper carries out the inversion for stress field of the source region by using MSATSI software. The inversion results show that the directions of all compressive stress axes are consistent to each other, but extensional stress axes exhibit strong inhomogeneity. Taking the 31.5°S as boundary, the south part is under approximately biaxial compression with major compression in E-W direction and minor compression in N-S direction, but extensional in U-D direction. Whereas in north part, the compressive axis is still in E-W direction, but the extensional stress axis gradually rotates to N-S direction.