According to known annual variations in the lithospheric magnetic field along the eastern segment of the Bayan Har block during the 2011-2014 period and crust stress data, the relationship between the lithospheric magnetic field and stress accumulation in the southern segment of the Longmenshan fault zone was studied. Annual variations in the lithospheric field in the local area was weaker than for surrounding areas during 2011-2012 and 2012-2013. High-stress accumulation was reflected in in-situ crust stress measurement after the Wenchuan M_S8.0 earthquake. Based on analysis of the piezomagnetic effect, it was concluded that the tectonic background of high-stress accumulation and low strain rate in the local area after Wenchuan M_S8.0 earthquake was the main factor controlling the weak variations in the lithospheric magnetic field. Additionally, the horizontal component of the lithospheric field in the area of the epicenter became weak before the Lushan M_S7.0 and Kangding M_S6.3 earthquakes. Both magnitude and direction of the horizontal vector for the 2012-2013 period differed across the surrounding area, which may be a precursor of two earthquakes.