The porous solar-driven interfacial evaporator has attracted substantial interest because of its high performance in converting solar energy into heat for water evaporation. However, the effect mechanism of porous structure (e.g., pore size and porosity) on water evaporation efficiency remains controversial and unclear, which largely restricts the design of high-performance solar evaporators. Herein, a porous solar interfacial evaporator with controllable porous structure was presented by integrating carbonized carboxymethyl cellulose with antimony doped tin oxide (ATO) powder (ATO-C). The experimental results revealed that reducing the porosity of ATO-C could reduce heat loss for heating the water inside channels, thereby improving the evaporation efficiency. Moreover, the synergistic light absorption of carbonized cellulose (in the visible region) and ATO (in the near-infrared light region) enable ATO-C to harvest a large fraction of sunlight (more than 98%) for water evaporation. On the basis, the ATO-C exhibited a water evaporation rate up to 1.44 kg m⁻² h⁻¹ under one solar irradiation with an evaporation efficiency of 90.38%, outperforming most previously reported solar evaporators. The current work clarifies the effect mechanism of porosity on evaporation efficiency, which helps to develop high-performance solar interfacial water evaporators.