Based on Coulomb static stress variation, the stress trigging action of the Mani ( M S 7 9, Nov. 1997) earthquake on the West Kunlun Mountains Pass ( M S 8 1, Nov. 2001) earthquake is researched. Results of different source mechanism resolutions show that a 10 -3 MPa Coulomb stress due to the Mani earthquake was added to the fracture fault of the Kunlun earthquake, and this may shift the broken date to about 10 years earlier, and infer that the stress level in the crust is not low. Comparing the relationship between strong earthquake strength and frequency and earth rotation change, it is shown that the strength’s decrease and the variation period’s shortening of earth rotation are important controlling factors on strong earthquake activity. This great event with M S =8 1 took place probably due to a gradual strengthening background of regional stress field within the Qinghai_Xizang block in the period of acceleration of change of day’s length and stress triggering from the Mani earthquake. Based on Coulomb static stress variation, the stress trigging action of the Mani (MS 7 9, Nov. 1997) earthquake on the West Kunlun Mountains Pass (MS 8 1, Nov. 2001) earthquake is researched. Results of different source mechanism resolutions show that a 10 -3 MPa Coulomb stress due to the Mani earthquake was added to the fracture fault of the Kunlun earthquake, and this may shift the broken date to about 10 years earlier, and infer that the stress level in the crust is not low. Comparing the relationship between strong earthquake strength and frequency and earth rotation change, it is shown that the strength’s decrease and the variation period’s shortening of earth rotation are important controlling factors on strong earthquake activity. This great event with MS = 8 1 took place probably due to a gradual strengthening background of regional stress field within the Qinghai_Xizang block in the period of acceleration of change of day’s length and stress t riggering from the Mani earthquake.