As an important infrastructure in transportation, aerospace, unmanned systems and other fields, the performance of Global Navigation Satellite System (GNSS) is directly related to the reliability of positioning and navigation services. The measured data from monitoring stations is taken as the research object and a set of methods on the analysis and evaluation of GNSS navigation performance is proposed, centering on four core indicators: accuracy, integrity, continuity and availability. Based on the analysis of measured data from monitoring stations, the strengths and weaknesses of the system across these four core indicators are summarized. The findings not only reveal the inherent limitations of a single GNSS but also theoretically and empirically demonstrate the critical value of multi-system fusion and augmentation technologies in enhancing service robustness, thereby providing a reference for the reliable use of GNSS in safety-critical scenarios.