Abstract: According to the fact that the Xinfengjiang reservoir earthquakes are caused mainly by water seepage, this paper, using the data of Ms2.0 earthquakes, studies the hydraulic diffusivity of the main- shock zone by the expansion of the distribution area of epicenters. It is indicated that in- situ hydraulic diffusivity during the preshock activity of the Xinfengjiang reservoir region was about 6.2m2/s. However, after the main shock, the in - situ hydraulic difiusivity in the main shock region increased by fifty percent, that is to say, to 9.7m2/s. During the long period after main shock occurrence the in - situ hydraulic difiusivity was affected by significant anisotropy of the medium and fluctuation of water level. No regularity can be found. In addition, we compare the difiusivity found by experiment with rock samples collected with the in - situ hydraulic difiusivity estimated. It is shown that the difiusivity of rock samples with fractures is about the same as the difiusivity estimated in- situ. However, the difiusivity of whole rock samples is 3 orders of magnitutes smaller than that estimated in - situ. Finally, we discuss the limits on the method by the expansion of distribution area of epicenters in the study of reservoir induced seismicity.