The utility model discloses a cooling device applied to a large transformer. The cooling device applied to the large transformer comprises a water storage container, a water pump and at least one heat sink unit and water-cooling units in one-to-one correspondence with the heat sink units; wherein each heat sink unit comprises at least one heat sink; the water-cooling units are formed by mutually communicating multiple cooling water pipes arranged on the upper side of the corresponding heat sink units; drain holes are formed in positions, at the upper side of the heat sink units, of each cooling water pipe of the water-cooling units; water tanks for collecting cooling water are arranged below the heat sink units; the cooling water pipes are communicated with the water storage container through the water pump; the water tanks are communicated with each other through a drain pipe; the water pump feeds the cooling water in the water storage container to the cooling water pipes and drains the cooling water out through the drain holes, and thus the heat sinks are cooled; the water tank collects the cooling water after the heat sinks are cooled and recycles into the water tank through the drain pipe. The cooling device applied to the large transformer has the advantages of high cooling speed, high cooling efficiency, good cooling effect, low equipment loss, low energy consumption and low use cost.