The invention discloses an electric energy metering electricity larceny prevention system and an electric energy metering electricity larceny prevention method. A voltage sampling circuit, a live wirecurrent sampling circuit and a zero line current sampling circuit are used to acquire voltage and current signals of a mains supply, and the signals are transmitted to an MCU; when the mains supply supplies power, the mains supply is directly used for supplying power to the MCU with the metering module function, and the MCU is used for monitoring the working state and the capacity of a rechargeable battery, when the power supply voltage at the input power supply side of the MCU is lost, a power supply switching circuit supplies power to the MCU by using the rechargeable battery, and when thepower of the rechargeable battery is completely consumed, the MCU is used for supplying power to the MCU with a standby battery, the MCU closes a built-in metering module and wakes up the built-in metering module every t seconds, if both the live line current and the zero line current are less than 0. 1A, the metering module continues to be closed, if one current is larger than 0. 1A, the apparentpower is calculated according to the current with the large sampling value, the metering function module is closed, the sampling frequency is high, and the sampling precision is high, so that the requirement of the 0.5-grade metering precision can be completely met.