Activity handover within engineering construction projects is time consuming, takes longer than the actual activities, and therefore, can cause duration delays. This paper presents relay chain seamless handover (RCSH) technology, which is based on relay technology theory and actor-network theory. This study systematically elaborated the RCSH processes, activity relay flows, and methods to address balancing speed under varying conditions. Our analysis results indicate that as compared to traditional activity handover, RCSH improves handover quality and guarantees the duration. RCSH technology was successfully applied in the third phase of the Three Gorges Dam Project, specifically for its concrete construction duration and quality control. Through the use of RCSH, effective overall planning, and efficient coordination of various production links, along with seamless activity handover in the third phase of the project were accomplished-with no additional time consumed by the handover process-and the construction of a concrete dam without a crack was achieved.