Abstract: As an important n-type semiconductor material, titanium dioxide is widely used in the research of pollutant degradation and catalytic hydrogen production in fields such as dyeing and printing wastewater, industrial wastewater, and pesticides due to its advantages of low cost, good stability, and non-toxicity. However, unmodified titanium dioxide often exhibits issues such as high photogenerated carrier recombination rates, narrow light response range, and inefficient interfacial charge transport in practical photocatalytic applications, significantly limiting further improvements in its catalytic degradation and hydrogen production performance. Therefore, optimizing the performance of pure titanium dioxide and overcoming existing limitations through modification methods has become a major research focus at present. This paper systematically elaborates on the basic mechanisms and applications of photocatalysis/photoelectrocatalysis, reviews the main research progress in modified titanium dioxide materials in recent years, focuses on summarizing modification strategies such as element doping, heterojunction construction, cocatalysts, and organic frameworks, and deeply analyzes the working mechanisms under different modification strategies. It also conducts an in-depth analysis of the underlying mechanisms under various modification approaches. Aimed at summarizing the application effectiveness and existing shortcomings of various modified titanium dioxide-based materials in enhancing wastewater degradation efficiency, selective pollutant removal, and hydrogen production, to provide reference for the rational design of subsequent high-efficiency, stable, and low-cost titanium dioxide-based photocatalysis/electrophotocatalytic materials and related research fields.