Abstract: After the installation of the pressure housing of the control rod drive mechanism (CRDM) in CEPR units, it was found that there were unqualified samples in the certificate test of CRDM welding. In order to shorten the period for the replacement of CRDM and reduce the impact on the overall progress of the project, a new pre-service inspection strategy is put forward by studying the pre-service inspection specifications in the process of the replacement of CRDM pressure housing. The practice shows that the off-line pre-service inspection of all CRDMs is completed within 10 days by using the optimized pre-service inspection scheme, which is about 20 days ahead of the original plan; through ultrasonic and eddy current inspection of some installed CRDMs, it is found that the results of off-line and on-line inspection are consistent, and there is no accessibility problem in on-line inspections.