The overcoring method used in deep borehole which was developed in the mid-term of 1980s has provided a large amount of measured data of geostress. Among these measurements there were only three times of measuring depth over 300 m. In the paper, after presenting the technique of this measuring method, the measured results of measuring depth over 300 m of the first time at the lock area of the Three Gorges Project(TGP) are introduced, and the geostress fields of this area are emphatically analyzed. At the same time, the measured results of other two times of measuring depth over 300 m for two practical engineerings are briefly presented. At last, measured results obtained by the overcoring method are proved by the data gained from the other boreholes of TGP’s lock area.