Abstract: The weld joint between reactor coolant pump（RCP） casing and steam generator is important pressure boundary,and the nozzle position tolerance of RCP casing will impact consecutive assembly of the RCP and pipe.This paper gives the example of the domestic first equipment fabrication,aiming at the welding deformation and easily nonconformance condition,and proposes some control measures avoiding the exceeding position tolerance due to serious weld deformation,such as RCP casing assembly alignment,weld preparation design and process control.The data shows that:the four as-built RCP casings according to the welding process,the discharge angle,angle of pitch between the main flange surface and the steam generator datum A and axes direction welding shrinkage is acceptable,and meet design requirements.