The measuring accuracy of the ZYZY-type Sea Gravity Meter,developed by Seis-mological Institute of State Seismological Bureau,was re-determined by sea gravity data that had been obtained during 1977-1979 in the study regions.The basic contours of free-air gravity anomalies,Bouguer anomalies and crustal thickness etc.were compiled.The characteristics of the crustal structures for the region in question were investigated with reference to geological and geophysical data.

In this paper,according to the horizontal dislocation patterns of the active fault and the composed features of deformation and fracture having taken place in the Cretaceous-Tertiary and Quaternary strata,related parameters of main stress axes (σ₁,σ₂ and σ₃) at the observed sites are obtained by means of the stereographic projection; and by combining with the data of focal mechanism,macroscopic earthquake phenomenon,crustal deformation and others,the tectonic stress field from the time of Himalayan movement is remoulded. It is show that,the axis direction (σ₁) of principal compressive stress in various tectonic zones of the Changjiang River and their related regions may have some tendency to evolve progressively,and may appear to be intersected state with time and space. During early and late neotectonic movement σ₁-axis of central faulting zone (A) in Hubei province is NNE-SSW and ENE-WSW,and at this same time,this axis in the southern segment of southwest tectonic zone (B) is NW-SE,but the northern position it is dominated by NNW-SSE In the eastern part of northwest tectonic zone (C),σ₁-axis direction is mainly NE-SW,while in its southwestern and northern segments this directron is under the control of NW-WNW-SE-ESE. In the recent stress field,σ₁-axis in the eastern portion of the (A) zone is NNE-SSW,in the western portion it is ENE-WSW,and the included angle between them is 40皁r so; σ₁-axis in the southwest (B)zone is NE-SW,but in the northeast part it is nearly N-S; in the whole (Ozone,ranges from NW-SE to WNW-ESE. with the obvious NE-SW principal compressive stress,It is quite evident that σ₁-axis distribution seems to be in the lack of uniform direction between or in the tectonic zones.According to "elastic rebound hypothesis" and "Boushinger effect",the relation shup between the alternation of σ₁-axis direction and seismicity of the Danjiang area is dealt with in the paper. Finally,the authors suggest that,in the tectonic stress field the alternation of σ₁-axis may be regarded as one of the seismogeological marks in the intraplate weak shock regions (or zones),based on the comparison of abovementioned features with the cases similar to relative stable segments of strong earthouake regions in North China and South-west China (for example Honghe River area).