Abstract: The earth's rotation and its speed change are important force sources of tectonic movement of the earth's crust.They have two kinds of horizontal primary forces-the force pressing from two poles to the equator and the f-orce on EW direction,the former is in direct proportion to square of angular velocity of the earth's rotation,the latter is in direct proportion to angular acceleration of the earth's rotation.The distribution of value of the two for-ces with latitudes is in accord with the distribution of large earthquakcs freq-uency in the whole earth with latitudes.The principal directions of tectonic stress caused by the two forces are consistent with the same principal stress directon in sources obtained from source mechanism of Ms≥6 earthquakes and with the statistical result of seismic belt strikes in the whole earth.1 per ce-nt of the energy which is caused by speed change of the earth's rotation is e-nough for earthquakes release.