Abstract: The shared understanding of law on movement of groundwater is that linear Darcy's law is the most basic equation of groundwater seepage. All the mathematical problems of groundwater flow can be derived based on Darcy's law if the the Reynolds number is less than a certain value between 1 and 10 (Re＜(1-10)). The experimental data obtained by Darcy are analysed again and similar seepage experiments are carried out with permeable stone porous media. Both results show that even though the Reynolds number is less than a certain value between 1 and 10 (Re＜(1-10)), the movement of groundwater would not obey Darcy's law but the nonlinear law. As the Reynolds number increases, the seepage friction grows gradually. It is concluded that Darcy's linear law is the approximate description of nonlinear law when the change of slope is small.