The utility model relates to a transformer substation accident oil pool, in particular to a single-cavity type transformer substation accident oil pool. The single-cavity type transformer substation accident oil pool is used for solving the problem that an existing accident oil pool is complex in structure and large in occupied area. The single-cavity type transformer substation accident oil pool comprises a cavity, a water collection pit, an oil inlet pipe and a water drainage pipe, the cavity is a cuboid space defined by six partitions, the oil inlet pipe and the water drainage pipe are fixedly arranged on the left side wall and the right side wall of the cavity respectively, the oil inlet end of the oil inlet pipe is communicated with a transformer oil pool of a transformer substation, the water collection pit is arranged at the position, on the water drainage pipe side, of the bottom of the oil pool, and the water inlet end of the water drainage pipe stretches into the water collection pit. A manhole is formed in the top of the oil pool, a cover plate covers the manhole, a ventilation pipe is further arranged at the top of the oil pool, and the two ends of the ventilation pipe are communicated with the cavity and the atmosphere respectively. The oil pool is provided with only one cavity, the occupied area and the size of the oil pool are reduced, and resources and cost are saved. The structure is simple, the volume of the cavity of the oil pool can be fully utilized for storing transformer oil, and application and popularization are facilitated.