Abstract: For one hundred earthquakes （5.0≤M_W≤6.9） that occurred around the epicenter of the 2010 Bio-Bío, Chile M_W8.8 earthquake from 1 January 1990 to 26 February 2010, their focal mechanism solutions were used to calculate the friction coefficient on the fault plane and the friction coefficient as a function of time. The results show that within the period of four years and two months from the beginning of 2006 until the occurrence of the Bio-Bío mainshock the friction coefficient around the epicentral area showed a decreasing trend, dropped from about 0.73 at the beginning of 2006 to about 0.4 immediately towards the occurrence of the Bio-Bío mainshock, with a relative decrease of 45.2%. It will be of great significance for understanding the occurrence process of strong earthquakes and earthquake prediction.