An electric energy meter power failure event active reporting method based a RS485 bus comprises the following steps: 1, when an electric energy meter power failure detection circuit detects a power failure, the electric energy meter closes other circuits besides the RS485; 2, the powerless electric energy meter monitors the RS485 bus communication state, enters step 3 if the RS485 is idle, otherwise enters the step 3 when the communicating data frames are finished; 3, in the electric energy meter communication gap, the powerless electric energy meter forcibly outputs the RS485 bus as a sending 0 state; 4, when other electric energy meters and acquisition terminals on the bus monitor the 0 state exceeds the 1-byte communication time, a power failure event waiting reporting state is entered; 5, when the acquisition terminal receives a sequence number sent by the powerless electric energy meter, the electric energy meter is tagged as the power failure state, and the power failure state is reported to the upper level terminal or the main station system. The method can realize power failure event active reporting on a half-duplex bus, thus greatly improving the responding speed in processing power failure events.