For the past decade in semiconductor manufacturing, technology of critical dimension (CD) metrology hasn’t been advancing as fast as CD downscales. As we reach the verge where metrology uncertainty rather than process capability start to be the bottleneck against tighter CD control, a thorough revisit on metrology tool condition control becomes crucial. CD-SEM in particular is on top of this list due to its complex and delicate physics, multiple-folds interaction with sample, destructive nature and its unique role in critical process development step such as OPC model calibration. In this work we focus on the characterization, evaluation and control of CD-SEM condition drifting aiming to keep current generation tool up with the higher metrology standard.