Abstract: Geomagnetic storms are a natural phenomenon that often occurs in the near-earth space. When a magnetic storm happens, the ionosphere fluctuates significantly,which leads to the reduction of the accuracy of ionosphere correction model and then affects the positioning result of single-frequency user. By using three stations’ observations of Harbin, Beijing and Sanya, we calculate the changes of ionosphere before and after a geomagnetic storm which occurs in April 2017, and then calculate the SPP results of dual-frequency mode, single-frequency basic navigation mode and single-frequency enhancement mode respectively. Comparing the results between different modes, and the results show that, during geomagnetic storms, the results of dual-frequency positioning are the best, and the results of single-frequency enhancement mode are slightly better than that of dual-frequency mode, and the two modes are generally superior to the basic single-frequency navigation mode.