Novel bulk ZnO porous nanosolids were prepared by a unique solvothermal hot-press method, using ZnO nanoparticles and several kinds of solvents as the starting materials. It was found from the experiments that ZnO nanoparticles underwent a "self-assembly process" under some specific hydrothermal hot-press conditions. As a result, some "nanoflowers" formed. The results showed that porous nanosolids with uniform pore diameters could be obtained when water distributed uniformly among the ZnO nanoparticles. On the contrary, if the uniformity of the distribution of water was poor, "nanoflowers" would appear in the water-rich region. It was also found that the photoluminescence of ZnO porous nanosolids was affected by the self-assembly phenomenon. In addition, the experimental results also showed that, both the volume and diameters of the pores could be adjusted by changing either the hot-press temperature, pressure or the kinds of solvents.