The invention relates to a floating dock underwater assembly technology. The floating dock underwater assembly technology is characterized by comprising the following specific technological steps of S1, ship segment, S2, launching, S3, self-loading control, S4, loading and ship moving, S5, total segment underwater assembly accuracy control, and S6, total segment underwater assembly. According to the floating dock underwater assembly technology, a whole ship is constructed independently, simultaneous construction can be conducted on different sites, and thus the construction period is shortened; as long as the dock conditions are adequate, construction is conducted by assembling together, and thus work after launching can be reduced; and a middle segment loads bow and stern segments, thus the demands for dock length conditions can be reduced, through loading construction, the dock utilization rate can be effectively increased, balance input of labor is facilitated, production plans arearranged flexibly and reasonably, the labor working environment can also be greatly improved, the way of entering a cabin of all major equipment is simplified, and the floating dock underwater assembly technology is of great significance to increasing of productivity of a shipyard.