Based on artificial tests of iced DC XZP-210 insulator strings carried out in the artificial climate chamber, the authors analyze the effects of units and assemble on the DC flashover voltage of iced insulator strings at high altitude districts. The test results show that the relationship between the DC icing flashover voltage and the insulator units is seemly linear with the increase of altitude or pollution level, although the linear relation is not obvious at the low altitude or pollution level. There is influence of the assembled form on icing flashover voltages, the flashover voltage of the horizontal string of iced insulators is highest while that of the vertical string is lowest. For various assembled forms, the effects of the air pressure on the flashover voltage of the horizontal string are most obvious.