Corncob is an extremely cheap and easily available biomass with excellent hydrophilicity. Crisscross pores of corncob provide channels for efficient water transport. An efficient solar evaporator is prepared by coating carbon black (CB) film on corncob. The light absorption of corncob coated with CB film is significantly enhanced, and the absorptance is more than 94% in solar waveband. The evaporation rate of CB-coated corncob is 1.425  kg/m²h, 78.1% higher than that of uncoated corncob. The height of corncob above water has an important influence on evaporation performance. The maximum evaporation rate is 1.88  kg/m²h when the corncob is 2 cm above water. Compared with 0 cm above water, the evaporation rate of corncob with 1, 2, and 3 cm above water increases by 13.7%, 32%, and 24%, respectively. The effect of light intensity on evaporation performance is studied. Although increasing the light intensity can achieve a higher evaporation rate, it will increase the complexity and cost of the solar evaporation device. With the advantages of rich raw materials and low cost, the corncob-based interfacial evaporator can reuse the crop waste. More importantly, the preparation method is very simple, and the whole process does not need to use complex mechanical equipment. This study will boost the applications of biomass materials in the field of solar vapor generation.