Abstract: After many investigations of the spouting abnormalies of underground water prior to earthquakes, "a two-dimensional radial symmetrical unstable infiltration flow model in single water layer under the action of pulse tectonic force" has been put forward as the precursor mechanism oi this kind of abnormaly.In this paper the corectness of the mechanism was quantitatively tested.On the basis of the theory, we inversed the rapid variation of local stress field prior to some earthquakes.For example, about 30 days prior to the earthquake of magnitude 4.3 occurred at Weijiaquan area of NE of wulumuqi on9 July 1979, the vertical component of underground stress aeted on water layer located in the depth of 1600m at No.Swell suddenly was increased by 1.3×10⁵Pa and after about several ten minutes it renewed;about 4 days prior to the earthquake of magnitude 5.3 occurred at the same area on 1 June 1983, the stress acted on the same water layer at No.5 well suddenly was increased by 4×10³Pa and after 11 hours and 40 minutes it renewed;and about 2 months prior to the earthquake of magnitude 6.5 occurred in the area on 13 November 1965, the stress suddenly was i ncreased by 1.7×10⁵Pa;and after everal ten minutes it renewed.These phenomena al so have been discussed in this paper.