FPSO is a kind of off-shore engineering equipment,which is designed as vessel type integrating production,storage and off-loading. There are various kinds of mooring system for FPSO. AS the most sophisticated mooring system,BMIT（bottom mounted internal turret） will be integrated into FPSO,mainly through welding. The requirement is very strict for both welding and dimension,any weld defect or out-of-tolerance will cause negative effect to overall performance of FPSO. This text details the quality control methods of integration welds.