Porous media are widely used in the production and living, and also in science and technology. With the development of energy, chemical industry, metallurgy, atomic energy and also with the progress of the modern industrial and agricultural production technology, a large number of heat and mass transfer problems in porous media gradually appear. Further promoting the development of the discipline about the formation and development of porous media becomes one of hot research points in the modern science and technology. It is expected that the accurate experimental picture and data can be obtained through the experiment, and the fluid flow picture and experimental data are analyzed in depth by using the corresponding software, so that the reliable data are obtained and the theory is supported intuitively, making the research of porous media more perfect. The experiment combined with particle image velocimetry technology and refractive index matching technique is conducted to test the transformation process of liquid flow in a random ball porous medium filled bed, and to extract the data. The extracted data are processed by using Tecplot software, and the transformation process of liquid flow mechanism is obtained. Experimental solid phase is a 25 mm-diameter crystal glass ball stacked bed, and liquid phase is the matching liquid prepared with the mixture of the 65% benzyl alcohol and 35% anhydrous ethanol. The refractive indexes of liquid phase and solid phase are both 1.477, which can successfully eliminate the laser light bending caused by the nismaching of refractive indexes. The flow field diagram in the pebble bed with Reynolds number Re in a range 4.7 Re 1000 is obtained experimentally. The comparisons of variations of flow field and flow lines among the different Reynolds numbers reveal that with the increase of Reynolds number, flow lines become more and more disorder: When the Reynolds number Rep exceeds 220, stable swirl flow inside the bed changes suddenly, and manifests a random feature in location and configuration, which forebodes its entrance into stable turbulence phase.