Pore structure characteristics have significant effects on the flow distribution, seepage characteristics, and reaction mechanism of the leachate as well as the uranium leaching efficiency in‐situ leaching (ISL) of uranium. In this study, a series of experiments including mercury injection and uranium leaching were conducted to study the characteristics of the pore structure and their effects on uranium leaching. The following conclusions can be drawn: The distribution of uranium‐bearing sandstone particle size shows the double fractal characteristic, and the particle size can be divided into coarse particles ( r > 0.6 mm) and fine particles ( r ≤ 0.6 mm). Furthermore, the pore volume and specific surface area of uranium sandstone both have dual fractal features corresponding to an intergranular‐dominant region and intragranular‐dominant region from mercury injection results. Fractures in the uranium‐bearing sandstone may be the main factors that lead to the abnormal fractal dimensions of pore structure. The uranium leaching efficiency of the sandstone increase with the leaching time and reach the maximum value (above 90%) at the 112th hour, and the whole leaching process can be divided into two phases taking the 60th hour as the demarcation point. Through correlation analysis, fractal dimension of the particle size, pore volume, and specific surface area was significantly correlated with the leaching efficiency of uranium at different dissolution phase. Corresponding measures such as adjusting solutions concentration and adding hydrofluoric acid can be taken to avoid the negative effect of pore structure. Those observations can provide a theoretical reference for the optimization of the leaching period and site design parameters of uranium‐bearing sandstone.