The photocatalytic transformations of CO2 into solar chemicals are a promising way in views of green energy and environmental sustainability. Improving the low catalytic performance and poor selectivity of the photocatalysts are one of the great challenges in this field. By mimicking the natural photosynthesis and taking advantage of the enzyme’s high specificity and efficiency, we designed the metal-free photocatalyst combined to an enzyme in order to synergistically solve the stated problems. In this work, we developed a metal-free polydopamine (P) modified sulfur-doped graphitic carbon nitride (P@SGCN) photocatalyst for the regeneration of NADH and the highly selective production of formic acid, HCOOH, from CO2. Our study shows a new way for the applications of polydopamine-modified photocatalysts to produce the solar chemicals/fuels from CO2.