In this study, a novel dynamic FMECA method based on Spherical Fuzzy Sets (SFSs) is proposed to address the limitations of traditional FMECA in the reliability analysis of CNC machine tools, particularly the issue of neglecting the dynamic changes of CNC machine tools due to service age. The proposed method integrates objective and subjective weighting by combining an SFS-based entropy weighting method with SFS-AHP, allowing for the management of expert fuzzy evaluations and a multi-perspective weighting of risk factors. SFS-based WASPAS is used to generate dynamic rankings at expert-suggested time points (1,000 hours and 10,000 hours), incorporating service age to provide age-specific failure mode rankings. The effectiveness of the method is validated through a case study on T-model CNC machine tools. The results show that failure mode rankings change with service age, demonstrating that this method provides more valuable insights for reliability-related decision-making, such as design improvements and maintenance planning.