Abstract: Non-closed watershed is a common phenomenon of karst regions,therfore it is essential to handle non-closed watershed when estimating karst water resoutce.The paper takes Houzhai experiment basin located at Puding county,Guizhou province as a case study to discuss the mechanism forming karst water.According to the surface and subsurface structures of the experiment basin,the paper develops a conceptual karst water model after dividing the experiment basin into four su卜basins and taking closeness degree of each sub-basin,which offers a new method to study non-closed karst watershed.