An anti-pollution-flashover locomotive roof composite insulator, comprising: a support body, and several groups of sheds arranged side by side along the axial direction that are set around the sidewall of the support body, wherein the sheds protrude out of the sidewall of the support body along the radial direction, the upper end of the uppermost shed is set with an upper metal fitting, and the lower end of the lowermost shed is set with a lower metal fitting. The creepage distance of the sheds between the upper metal fitting and the lower metal fitting is 1085 mm-1095 mm, and the arcing distance between the upper metal fitting and the lower metal fitting is 245 mm-255 mm. The insulator employs a long specific creepage distance in terms of structural design, thus providing a good pollution flashover resistance, and under the same pollution condition, a good pollution flashover resistance that is over twice of that of a porcelain insulator with the same creepage distance may be obtained, and hence it is especially applicable for moderate and serious polluted regions.