The utility model relates to an external insulation device for freezing pipes, which is most suitable for thermal insulation for freezing pipes in a non-freezing section of an artificial stratum freezing project. A sleeve covers a freezing pipe in a freezing section to serve as a protective layer, a heat radiation prevention layer is arranged inside the protective layer sleeve, steel connecting plates are arranged between the two ends of the sleeve and the freezing pipe to form an airtight gas heat insulating layer, and holes for discharging water or gas are arranged on the connecting plates. The utility model can greatly reduce coldness loss and effectively reduce freezing cost with simple structure, reliable effect, convenient construction, material saved, low cost and good thermal insulation effect, thereby having wide practicability.