The invention relates to an automatically switching device for the economical parallel running of remotely-mounted distribution transformers, comprising a current signal detecting, judging and processing circuit, a time delaying circuit, a signal transmitting circuit, a distribution transformer switching on circuit and a distribution transformer switching off circuit, wherein the output ends of the current signal detecting, judging and processing circuit are large constant current value end and small constant current value end which are respectively connected with the distribution transformer switching on circuit and the distribution transformer switching off circuit. When a current detecting circuit detects that the current value exceeds the set large constant current value, the distribution transformer switching on circuit is started by delaying time, and one distribution transformer is automatically made to run. When the current detecting circuit detects the small constant current value, the distribution transformer switching off circuit is started by delaying time, and one distribution transformer is automatically made to stop running. The automatically switching device can automatically switch accurately in time according to the electricity utilization load and the set economical distribution transformer running mode so as to reduce the non-load loss of the distribution transformers. The automatically switching device can be used for the economical parallel running of the remotely-mounted primary and secondary distribution transformers so as to omit the complex and onerous switching operation and the of the maloperation by the worker and effectively reduce the loss of the power grid.