Abstract: To analyze the disturbance patterns in the ionosphere and the changes in GPS positioning performance during magnetic storms, based on the IGS (International GNSS Service) global observation data and the GIM (Global Ionospheric Map), we conducted an analysis of the abnormal variation of total electron content (TEC) in the Northern Hemisphere during the geomagnetic storm event on August 26, 2018, as well as the GPS positioning performance. The results show that the TEC anomalies in the Northern Hemisphere exhibit latitude differences, with faster responses in higher latitude regions and larger variations in lower latitude regions, reaching up to 12 TECU (total electron content unit). During the magnetic storm, significant cycle slips were observed in the higher latitude regions, with a maximum decrease of 61.84% compared to magnetically quiet days. The data integrity of all stations decreased during the storm, with higher latitude regions experiencing a faster and more severe decline, reaching 38.65%. The decrease in data integrity of all stations occurred during the recovery phase of the storm. The data quality is consistent with the pattern of TEC anomalies. Analyzing the results of GPS dual-frequency dynamic precise point positioning (PPP), it was found that the positioning errors at higher latitude stations during the magnetic storm significantly increased, with horizontal and vertical root mean square errors reaching approximately 0.7 m and 1.8 m, respectively.