Abstract: The tectonic blocks show the characteristics of integral movement during the crustal movement and under dynamic process of the Earth.It shows that the dynamic characteristic direction is distributed with regionalizaion. Thus, the stress field characteristic direction of each block is similar with the main structure force direction where strong earthquakes happen.The stress non-uniformity and accumulation of energy on the boundary or in certain parts of some blocks appear.The sign when the lineal accumulation transforms to the non-lineal critical situation comports at this echo that the weak seismic activity associated with the solid tide alternating stress field along the main tectonic direction.The medium fatigue strength increases in an alternating stress field, and then some weak events are triggered.So the seismic frequency proportion is maladjusted when the appendant stress field direction is positive or negative main tectonic direction;this also indicates the coherence of most foreshock mechanism.Using this idea of stress modulating action the data of North China region and Yunnan province are analyzed by three ways.The result indicates that it is significant for long-and medium-term prediction.The R-value is bigger than 0.5.

Key words: Tectonic stress field, Appendant solid tide stress field, Modulation