The utility model relates to a transformer core for single-phase direct-current magnetic bias experiments. The transformer core is of a single-phase three-limb structure, and comprises fastening components and a core body arranged between the symmetrical fastening components. The special structure of the core body ensures that the transformer core can decrease no-load current to the max in order to benefit a direct-current experiment; meanwhile, the width of each yoke is also increased to the max, the size of each core clamp is enlarged, so that the eddy-current loss in the clamps can be increased, and thereby the hot-spot temperature of the clamps can be conveniently monitored.