Abstract: The positioning accuracy of the GNSS is crucial for numerous key applications in modern spatio-temporal information services. Satellite orbit errors, as one of the main error sources of GNSS, have complex propagation mechanisms and spatial correlations, which are the key factors limiting the performance of high-precision positioning. This paper establishes geometric models of orbit errors for both GNSS single-point positioning and relative positioning accuracy, and elaborately deduces how orbit errors affect the final positioning results. It respectively presents the quantitative formulas for single-point positioning errors and relative positioning errors under the influence of orbit errors. Combined with practical calculation examples of precise single-point positioning and relative positioning, the correctness of the theoretical deduction is verified: the single-point positioning accuracy is directly related to the magnitude of orbit errors and the position dilution of precision (PDOP), while relative positioning can effectively reduce the influence of orbit errors through differential processing. This study aims to deepen the understanding of the action mechanism of orbit errors and provide a solid theoretical basis and valuable practical reference for the suppression of orbit errors in GNSS data processing and the further improvement of positioning accuracy.