This paper briefly presents the principles of piezomagnetic stressometers, repeated observation and experiment results under hydro-pressure in crust rocks. It was expounded that the values measured by suspended element were compared with those by forced element. The crustal stress changes and the micro displacement of fault were ynchronously rippled. That the similar crustal stress changes were measured in the corresponding period at the stations ten to hundreds km apart. In the regions of few earthquakes the crustal stress were stable, and that earthquakes was predicted successfully many times by anomalies of crustal stress, we found and proved that the direction of anomalous principal stress is pointed at or mined to epicenters, the stations with higher anomalous principal stress were near the epicenters, and the duration time of long-termanomaly was linearly related with the magnitude of earthquakes. It has been demonstrated that we can measure the process of change of stress field with the gauges in the borehole and make time, location and magnitude prediction for earthquakes. It has been 50 years since the method was used for the study of the premonitory stress observation and earthquake prediction under the late proposition of Prof. J. S. Lee and under the concrete direction of Academician Chen Qingxuan.
Prof. J. S Lee. a famous Chinese scientist, put forward that: The cause of earthquakes is due to an underground force which pushes the rocks in the crust. Therefore, based on the research of the active structure system, to select proper sites and observe the process of stress changing, strengthening, and reaching the breaking point is ensured by the system under the condition of different tectonics and rocks, how high its sensitivity is, how the observation error and the stability in a long period are.