The invention relates to a meter box and a system capable of estimating an error of an intelligent electric meter online. A metering chip is embedded into a main switch of the meter box, equivalently,a metering unit is added into the main switch to serve as a main meter of all meters of the meter box, and thus, line loss can be reduced to the maximum extent. The main meter and sub-meters are located in the same meter box, factors influencing line change are little uncertain, impedance of lines is very low, and influence of load fluctuation on line loss can be neglected, and line loss can be almost fixed. A regression equation is fit by using a regression algorithm, the existing fixed loss in the meter box can be calculated, and the remaining represents a metering error of the electric energy meters.