Bushing is one of the important equipment in substation. There have been some researches on the flashover of bushing at high altitude, but there are few researches on composite bushing. This paper studied the DC composite bushing pollution flashover characteristics under high altitude conditions through the test and analysis in artificial climate chamber. The results show that when the altitude increases, the pollution flashover voltage will decreases, and decreases with the increase of ESDD (Equivalent Salt Deposit Density). At the same time, the dry arc distance and creepage distance of the composite bushing are also given, and will provide information for the bushing insulation design under high altitude DC conditions.