The invention discloses a gallium nitride series CIGS device for artificial photosynthesis and a preparation method thereof. The device includes a TCO layer, a ZnO layer, a CdS layer, a CIGS layer, a Mo layer, an In layer, a GaN layer, an n+-GaN layer, and a sapphire layer sequentially from bottom to top. The preparation steps are as follows: place a GaN film on a clean glass sheet, place In particles evenly on the surface of the GaN film, after placing, place a CIGS solar cell on the surface of the In particles, press it flat, put a clean glass dish on the surface, and put It is put into a vacuum drying oven, evacuated, heated for a period of time, and cooled to room temperature to obtain a gallium nitride series CIGS device. Compared with Si-based GaN devices, the device of the present invention is energy-saving and environment-friendly, and has a simple process. Using the present invention as an anode for photosynthesis has the advantages of high photocurrent density and high cathode potential, and has a strong light absorption coefficient, which is beneficial to solve the development and utilization of new energy and the protection of CO 2 governance of environmental issues.