Water drain device for accident oil pool of box-type substation

The invention relates to a water drain device for an accident oil pool of a box-type substation. The water drain device comprises a water drain pipe connected to a water drain outlet of the accident oil pool, a plurality of filtering layers sequentially arranged in the front end of the water drain pipe, a sealed water tank, a water storage pond, a piston type driving mechanism, a siphon communicating the sealed water tank and the water storage pond, a downcomer connected with the tail end of the water drain pipe and extending to the water storage pond, and an automatic water outlet arranged inthe bottom of the sealed water tank, wherein the sealed water tank and water storage pond are sequentially arranged. The piston type driving mechanism comprises a cavity arranged to be crossed with the middle section of the water drain pipe and communicating with the inside of the water drain pipe, and further comprises an upper sealing part, a connecting rod and a lower sealing part which are arranged in the cavity in t