The recent surge of alternative clean energy with minimal environmental impact in a cost-effective way requires the exploration of new materials and/or structures as efficient electrodes for industry-level photoelectrochemical (PEC) water splitting into usable H₂ fuel. It is well-known that nanomaterials could outperform their bulk counterparts in many aspects because of increased interacting sites, shorter lateral diffusion distance and lower reflectivity. Assembling nano-building blocks into desirable structures is a more advanced intelligent tactic for realizing higher performance and better functionality by exploiting new hierarchy and scaling-up laws. To meet the challenges, hierarchical 3-D nanostructures integrating 1-D conduction trunks and secondary branches, e.g. dendritic nanowires (NWs)/nanofibers (NFs), are particularly desired in light of the greatly improved light-harvesting, the efficient charge separation and short hole diffusion length (L_D) for which the refined secondary structures are responsible. In terms of methodology, a seeding method in solution phase still confronts some engineering obstacles notwithstanding it being regarded as a major avenue to fabricate heterogeneous nanostructures of semiconductors. To elevate the spatial occupancy of one-dimensional ZnO nanostructures and overcome the limitations of multistep seeding method currently widely used, a rational, facile and high-yielding procedure will be presented here for the fabrication of the interconnected three-dimensional “caterpillar-like” ZnO nanostructured networks (CZNs) for photoelectrochemical applications. Moreover, by fine-tuning the synthesis procedure and manipulating their growth process, the dependence of their photoelectrochemical properties on geometry factors of these unique CZNs consisting of branched ZnO nanowires onto ZnO nanofibers with tunable surface-to-volume ratio and roughness factor has been investigated. They offer mechanically and electrically robust interconnected networks with open micrometer-scale structures and short hole diffusion length. The preferential light-material interaction and charge separation to maximize the photo-to-hydrogen conversion efficiency were further studied. When used as photoanode, our CZNs not only favor sunlight harvesting with multireflection ability, but also suppress the recombination of photogenerated charge. Compared to the literature results, our CZN photoanodes with ZnO nanobranches of ~2.2 μm in length and ~25 nm in diameter exhibited the highest photocurrent density of 0.72 mA∙cm^-2 at +1.2 V (versus Ag/AgCl) and conversion efficiency of 0.209% at +0.91 V (versus RHE) without being decorated with noble metal cocatalysts or nonmetallic/metallic dopants due to their favorable structural features. Overall, our procedure to obtain the desirable CZN provides great opportunities for facile and efficient fabrication of model photoelectrochemical anodes and would be applied to other materials for sustainable chemistry and engineering applications.