Underwater robots have emerged as key tools for marine exploration because of their unique ability to traverse and navigate underwater regions, which pose challenges or dangers to human expeditions. Miniature underwater robots are widely employed in marine science, resource surveys, seabed geological investigations, and marine life observations, owing to their compact size, minimal noise, and agile movement. In recent years, researchers have developed diverse miniature underwater robots inspired by bionics and other disciplines, leading to many landmark achievements such as centimeter-level wireless control, movement speeds up to hundreds of millimeters per second, underwater three-dimensional motion capabilities, robot swarms, and underwater operation robots. This article offers an overview of the actuation methods and locomotion patterns utilized by miniature underwater robots and assesses the advantages and disadvantages of each method. Furthermore, the challenges confronting currently available miniature underwater robots are summarized, and future development trends are explored.