Abstract: The new bucket structure breakwater is one kind of deepwater offshore structure in the open sea area. The settlement monitoring of the bucket structure has been a major problem in the in-situ tests. Combined with the in-situ tests of the structure, the settlement measurement technology of offshore deepwater structure is investigated, and the settlement measurement can be achieved using the photoelectric encoder. According to the comparison with the synchronized results of GNSS deformation monitoring system, it is proved that it is feasible to use the photoelectric encoder to measure the settlement of offshore deepwater structure, and the measurement accuracy is mainly affected by the inclination of the measured structure. An automated test system is developed for open offshore deepwater structure, which realizes settlement measurement and data transmission.