Abstract: Leaching area is one of the important factors that must be considered in economic and technical evaluation of in-situ leaching of uranium.Because the leaching process is taken place in the ore bed underground,it is difficult to determine the leaching area.In this paper,based on study of the in-situ leaching process of a mining unit at a sandstone type uranium deposit in northwest China,a new method for leaching area calculation by using particle tracer technique which is employed in Modpath as a model integrated in Visual Modflow was explored.According to the hydrogeological conditions and leaching flux data,lixiviant flow was simulated by using Visual Modlfow and the flow distribution was showed by the tracer paths,which gave us information about the flow directions,velocities and paths of lixiviant.Different path had different contribution to the total extraction flux,so,the contribution of each path had been calculated and ordered from low to high,and the lowers of which cumulative contribution ratio achieved 5% were wiped off,thus,the leaching area was determined by the highers of 95%.According to this method,the calculated leaching area was 1.51 times to geometric area of enclosure of mining wells.