Metal oxides play an essential role in mode optoelectronic devices because they have many unique physical properties such as structure diversity,superb stability in solution,good catalytic activity,and simultaneous high electron conductivity and optical transmission.Therefore,they are widely used in energy-related optoelectronic applications such as photovoltaics and photoelectrochemical (PEC) fuel generation.In this review,we mainly discuss the structure engineering and defect control of oxides for energy applications,especially for transparent conducting oxides (TCOs) and oxide catalysts used for water splitting.We will review our current understanding with an emphasis on the contributions of our previous theoretical modeling,primarily based on density functional theory.In particular,we highlight our previous work:(i) the fundamental principles goveing the crystal structures and the electrical and optical behaviors of TCOs;(ii) band structures and defect properties for n-type TCOs;(iii) why p-type TCOs are difficult to achieve;(iv) how to modify the band structure to achieve p-type TCOs or even bipolarly dopable TCOs;(v) the origin of the high-performance of amorphous TCOs;and (vi) band structure engineering of bulk and nano oxides for PEC water splitting.Based on the understanding above,we hope to clarify the key issues and the challenges facing the rational design of novel oxides and propose new and feasible strategies or models to improve the performance of existing oxides or design new oxides that are critical for the development of next-generation energy-related applications.