The invention provides an expansion heat dissipation device of an out-planet single-machine. The expansion heat dissipation device comprises a heat dissipation substrate, secondary surface mirrors, thermal-control coatings and a heat dissipation paste layer. The secondary surface mirror is arranged on the outer surface of the heat dissipation substrate. The heat dissipation substrate is provided with a single-machine installation region. The heat dissipation paste layer is arranged on the external surface, corresponding to the secondary surface mirrors, of the single-machine installation region. The thermal-control coatings are arranged on the external surfaces of the secondary surface mirrors, opposite to a to-be-installed single machine, of the heat dissipation substrate. The heat dissipation substrate is a U-type aluminum plate. According to the invention, by arranging the secondary surface mirrors, normal working temperature of a spacecraft can be effectively maintained; and the heat dissipation paste layer is arranged on the external surface, corresponding to the secondary surface mirrors, of the single-machine installation region, so heat of the to-be-cooled single machine can be effectively transmitted to the heat dissipation substrate.