The establishment of low voltage metering current transformer automatic testing system (referred to as the assembly line) eliminates manual errors in the calibration process of low voltage current transformers, improves work efficiency and economic benefits. However, its characteristics of no manual intervention throughout the entire process and long-term continuous operation also bring new challenges to metrological technical supervision and quality monitoring. This article analyzes the quality monitoring methods and proposes a control chart quality monitoring method suitable for low voltage current transformer assembly lines. By establishing a mathematical model of the assembly line control chart, introducing an overall error criterion for the assembly line, and using inspection data from inspection standards on the assembly line, a control chart for the operation status of the assembly line was established. This ensures that the measurement process and performance of the assembly line are always under control, achieving online measurement technology supervision and quality monitoring of the assembly line.