Abstract: As a Class Ⅱ medical device, clinical mass spectrometers face challenges in performance stability when operating in long-term, high-volume, and high-matrix clinical application scenarios. However, a unified standard method for evaluating performance stability has not yet been established domestically or internationally. This study aims to construct a scientific and universal evaluation system for the key performance stability of clinical mass spectrometers based on the Statistical Process Control (SPC) theory, providing technical support for the access review of regulatory authorities and the quality improvement of manufacturing enterprises. Firstly, based on the division of clinical application needs and risk levels, key performance parameters such as detection limit and anti-interference capability, as well as their importance levels, are determined. Key performance data are collected by simulating actual clinical operating scenarios, and the X-bar-R control chart is used to judge the statistical steady state. The Stability Capability Index (SCI) is constructed the Process Performance Index (PPK) as the core to complete the technical steady state evaluation. Finally, the stability levels are classified through the combined determination of statistical steady state and technical steady state. The effectiveness of the method is verified through the detection limit test using ICP-MS. The results show that this method can not only effectively evaluate the key performance stability of the instrument but also identify the root causes of instrument performance fluctuations. The conclusion indicates that the SPC-based method for evaluating the key performance stability of clinical mass spectrometers is scientific, operable, and economical. It can not only accurately predict the performance degradation trend of instruments and warn of failure risks but also provide a unified standard for the whole-life cycle quality control of medical devices. It is applicable to the stability evaluation of different types of clinical mass spectrometers and is of great significance for standardizing industry quality standards and improving clinical application safety.