The invention belongs to the technical field of switching power supply protection, and relates to a power supply detecting and switching device for an electric energy meter. The power supply detectingand switching device comprises an MCU chip unit, an auxiliary power circuit unit, a main power circuit unit, a power-off meter-reading battery circuit unit, a clock battery circuit unit, a DC/DC circuit unit, a dummy load circuit unit, a first voltage detecting circuit unit, a second voltage detecting circuit unit, a first P-channel MOSFET circuit unit, and a second P-channel MOSFET circuit unit.A power supply detects whether the first voltage detecting circuit unit, the second voltage detecting circuit unit and the DC/DC circuit unit are powered on. The MCU chip unit detects the levels of the first voltage detecting circuit unit, the second voltage detecting circuit unit and the DC/DC circuit unit. When the main power circuit unit is powered off, the power supply automatically switchesto the power-off meter-reading battery circuit unit, and the MCU chip unit is in a low-power mode. When the power-off meter-reading battery circuit unit has no power, the power supply automatically switches to the clock battery circuit unit for power supply.