In order to improve the availability and operating efficiency of the DC system, Qi-Shao ± 800 kV UHVDC transmission project pole layer control system is equipped with two kinds of fault restart function, namely the instantaneous fault restart and the valve group fault restart. The triggering mechanism, timing and opening conditions of these two restart logic are analyzed in detail, and the relationship between the instantaneous fault restart logic and other protections reacting transient fault in pole and bipolar zone is studied emphatically, DC system debugging scene recorded wave diagram is referred to illustrate the two restart logic of the action process and effect. The research can provide some guidance and reference significance to the field operation and research work. This work is supported by Science and Technology Project of State Grid Hunan Electric Power Company (No. XDKY-2016-015).