Abstract: With the increasing demands for ship stealth performance and onboard comfort, the 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 constrained by spatial limitations and coupling interference in ships, while indirect testing technology based on the reciprocity principle offers a novel approach to address these challenges. This paper systematically reviews the theoretical progress and engineering practices of reciprocity testing for ship mechanical-acoustic systems: Firstly, it introduces the historical development of reciprocity testing theory and the current status of engineering applications. Secondly, 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. Then, the "relative accuracy" reciprocity testing concept is illustrated through a case study of ship radiated noise directivity testing. Finally, the paper provides an outlook on critical issues requiring urgent resolution in the engineering application of reciprocity testing for ship mechanical-acoustic systems.