Abstract: To improve the long-wave timing accuracy, the factors were analyzed that affected the errors of ASF. In the progress of calculated the ASF by Millington algorithm, experiments were designed to point at the errors of the map location, the ground conductivity and the region segmentation, then, collected data and analyzed the results. Finally, the new methods to reduce the errors of ASF put forward.

Key words: Long-wave time service, Additional second-phase factors (ASF), Ground conductivity, Transition region