The maintenance of reactor body is an important work that must be done in refueling overhaul of nuclear power units.Due to the complex structure,large size,tight maintenance period and high radiation dose rate of the equipment in the reactor body,it is very difficult to measure and inspect defects and install and locate underwater maintenance tools,which cannot be measured and inspected with conventional techniques.In this study,advanced high-precision laser measurement technology based on spherical coordinate method combined with flexible tooling can realize accurate underwater long-distance measurement in large space.The trend of the measured data can be analyzed,and the reasons for the deviation are obtained,which can provide reliable data support for the overhaul of the unit,thus ensuring the smooth execution of underwater maintenance work in high radiation environment and ensuring the safe,reliable and stable operation of the nuclear power plant.