Nuclear reactor pressure vessel is the heart of nuclear power plant. The surfacing quality of main bolt hole is related to the normal operation of reactor pressure vessel, and will affect the operation safety and operation time of nuclear power plant. Aiming at the unqualified PT/UT detection problem of main bolt hole surfacing in the manufacturing process of reactor pressure vessel in a factory, the causes of welding defects are analyzed as follows:（1） Unstable arc in local area and poor protection of weld area;（2） Poor welding station makes it difficult for welders to operate. The corresponding improvement measures are put forward, such as changing manual surfacing to mechanical argon arc welding,and changing flame heating to electric heating plate heating;conduct targeted training on workpiece status; strengthen the cleaning of the surface to be welded and strengthen the operation requirements. After field verification, the above measures have significantly improved the first pass rate of main bolt hole surfacing PT/UT, and provides valuable technical accumulation and engineering experience for the manufacturing of RPV in subsequent projects.