Photoreduction of CO2 into valuable fuels is a clean and sustainable way to mitigate the energy crisis and environmental problems. Factors limiting the efficiency of CO2 photoreduction include narrow-band light absorption, poor charge carrier separation and transport, and sluggish activation/reaction of CO2 on the surface of photocatalyst. In recent years, defect engineering of photocatalysts emerges as an effective method to improve their efficiency in the photocatalytic conversion of CO2 into useful fuels. This review is focused on discussing how structural defects can be used to modulate the electronic structure of the photocatalysts and activate the inert CO2 molecules. Special emphasis is placed on the important impact of defects on the charge carrier dynamics of the photocatalysts. Our discussions cover a variety of defective semiconductors, including metal oxides, metal sulfides, and two dimensional materials. In addition, the challenges and prospects of defect engineering in photoreduction of CO2 are also analyzed. This review aims to provide useful information about the fundamental principles of photoreduction of CO2 and guidance on the design and preparation of defective photocatalysts.