The invention discloses an oil-water separating sewage drain device for a transformer oil reservoir. The device is characterized by being composed of an oil reservoir water level determination device (1), an integrated control device (2) and a sewage drain device (3); the oil reservoir water level determination device (1) comprises a supporting rod substrate (1-10), an adjustable supporting rod (1-2), a zero potential contact chip (1-1), a sewage drain pump start contact chip (1-3), and a sewage drain pump stop contact chip (1-4); the integrated control device (2) comprises a control device body (2-13), a power switch (2-6), a liquid crystal display (2-5), and an F21-E1RX remote control device (2-14); the sewage drain device (3) comprises a sewage drain pump (3-1) and a voltage-sensitive relay CJXZ-2510 (3-2). According to the oil-water separating sewage drain device for the transformer oil reservoir, water in the transformer oil reservoir is monitored in real time and drained in time, therefore, the occurrence of an accident that the surrounding environment is damaged due to occurrence of overflow of transformer oil when the oil reservoir is waterlogged is prevented, and the labor intensity of operation and maintenance staff as well as operation and maintenance cost of the device are reduced.