The invention relates to an electric energy meter metering error online monitoring circuit based on CT sampling, which is characterized in that the circuit is composed of three current transformers, an alternating current source, three programmable gain amplifiers, three analog-to-digital converters, three low-pass filters 1, three low-pass filters 2, three high-pass filters and an error monitoring module. The invention also relates to an electric energy meter metering error online monitoring method based on CT sampling. The electric energy meter metering error online monitoring circuit and method based on CT sampling is scientific and reasonable in design, has the advantages of improving the detection efficiency, saving manpower and material resources, being accurate in metering, stable and reliable and the like, and is a highly innovative electric energy meter metering error online monitoring circuit and method based on CT sampling.