The energy crisis and environment pressure have driven people to search for a sustainable way for society to develop. To achieve this goal, artificial photosynthesis is a promising choice, where the CO2 reduction reaction (CO2RR) happens on a semiconductor catalyst driven by sunlight. CO2, viewed as a nasty waste product, can also serve as an available carbon source to produce value-added chemicals (e.g., methanol, ethylene, formic acid and so on) through the CO2RR. In pursuit of high efficiency for the CO2RR, it is essential to design effective and stable semiconductor photoelectrodes via optimizing the light harvest, charge separation and transfer, and surface reaction. Besides the efficiency, CO2RR also faces other challenges including CO2 solubility and product selectivity. In this chapter, we will discuss these issues from three aspects of the photoelectrochemical (PEC) process: the physico-chemical process at the photoelectrode, the surface co-catalyst choice, and the influence of the electrolyte solution.