Abstract: With increasing demands for enhanced ship stealth performance and onboard comfort, precise quantification of vibro-acoustic characteristics in complex ship systems is critical for optimizing structural acoustic design and reducing radiated noise. Traditional vibro-acoustic measurement methods are limited by spatial constraints and coupling interference within ships, while indirect testing technology based on the reciprocity principle offers a promising solution to these challenges. This paper provides a comprehensive review of the theoretical advancements and engineering practices of reciprocity testing for ship mechanical-acoustic systems. First, it introduces the historical development of reciprocity testing theory and the current status of its engineering applications. Second, it analyzes and summarizes the key technical challenges hindering the industrial application of reciprocity testing, focusing on error-influencing factors and low-frequency, high-power acoustic sources. The concept of "relative accuracy" in reciprocity testing is then demonstrated through a case study on ship radiated noise directivity testing. Finally, the paper discusses critical issues that need to be addressed in the engineering application of reciprocity testing for ship mechanical-acoustic systems.