The invention provides an automatic switching device for the economic operation of a power transformer, comprising a current signal detection circuit, a current signal judgment processing circuit, a time-delay circuit, a transformer switch-in closing circuit and a transformer switch-off tripping circuit; wherein the current signal detection circuit is connected with the current signal judgment processing circuit; the current signal judgment processing circuit outputs a large fixed value termination point and a small fixed value termination point which are respectively connected with the transformer switch-in closing circuit and the transformer switch-off tripping circuit through the time-delay circuit; when the current detection circuit detects that a current value exceeds a set large fixed value, the closing circuit is started in a time-delay way, and a transformer is automatically switched in for operation; and when a small fixed value is detected, the tripping circuit is started in a time-delay way, and the transformer is automatically switched off for the operation. The automatic switching device can accurately automatically finish the switching in time according to a set economic operation way of the transformer, be used for the parallel operation of the transformer and the operation of a main transformer and a sub-transformer, reduce the complex and heavy switching operation and the misoperation of workers and the operation loss of a power grid and enhance the enterprise and society benefits.