Abstract: Pigsty cleaning has been one of the most crucial working links in the treatment of manure and sewage in pig farms. The health status of pig herds can depend mainly on the cleaning performance. However, the current manual cleaning of pigsties cannot fully meet the large-scale production in recent years. It is also required for long-term exposure to higher humidity and concentrations of harmful gases inside pigsties, such as ammonia and hydrogen sulfide, compared with the outdoor environments. Moreover, manual manure cleaning has been the more unfavorable activity with an adverse impact on physical health, due mainly to the high labor cost and intensity. Some stress can also be likely to affect animal welfare during manual cleaning. Therefore, cleaning robots can serve as an effective solution to replace manual operations in the future. This study aims to review the research and application progress of manure-cleaning robots in the modern management of pig farms. Three perspectives were also set: the cleaning scene requirements and spatial operation of pig farms, the flushing of empty pig pens, the manure cleaning on the ground of pigsties with pigs present, and the cleaning of underground manure ditches. The key technologies of pigsty cleaning robots were also involved in multiple aspects, including application scene, chassis types, driving modes, position, and navigation, as well as path planning, manure cleaning mechanisms, and manure identification. The flushing robot of the pigsty empty pen was used to clean the floor and pen facilities of pigsties after each batch of pigs was removed under the "all in and all out" management mode of large-scale pig farms. The chassis type was then classified into the wheeled and tracked one. Among them, the wheeled chassis was often combined with mechanical arms and high-pressure water guns, predominantly suitable for flushing operations in the aisles of pigsties. The ground manure cleaning robot in pigsties with pigs was designed for the daily cleaning of residual manure on the floor inside the pen or on the aisle of the confinement stalls. Therefore, it was required for accurate manure identification and positioning, navigation, and path planning. Meanwhile, the effective manure cleaning included the scrape-shovel and manure collection, according to the materials of the slatted floors in pigsties. The underground manure ditch was characterized by its narrow space and dim lighting. Therefore, the cleaning robot was adopted to replace the manual cleaning and the frequently malfunctioning manure scraper. A tracked chassis was combined with the high-pressure water flushing and shovel operation. Residual manure was regularly removed in the manure ditch, in order to ensure a better air environment in the pigsty. Some suggestions were given to focus on the research of cleaning robots, according to the current development and deficiencies of Chinese pigsties. A special chassis can be developed with lightweight, excellent load-bearing and off-road capabilities suitable for pigsty cleaning scenarios; An independent environmental perception and operation can also be required in the path planning system; The durable sensors resistant to moisture and corrosion are suitable for the harsh environment of pigsties; A digital collaborative management and control platform can be established to realize the collaborative work of multiple intelligent agents, such as pigsty cleaning robots; and automated facilities are also complementary to cleaning robots. Some emphasis can then be put on the pen and pigsty cleaning robot in the concept of welfare and healthy breeding. The finding can also provide a strong reference to promote factory-based, unmanned, and welfare-oriented intelligent pig breeding.