Since 2014, the automatic testing system of electric energy measuring instruments has been applied on a large scale in various provincial companies, and effectively supports the verification and testing of electric energy measuring instruments. According to the existing regulations and specifications, the traceability of the automatic testing system needs to stop work and disassemble the standard equipment, and the repeated disassembly and assembly accelerates the aging of the contact points and affects the overall measurement performance of the verification system. Secondly, the frequency of inspections during the period is low, and once the standard is inaccurate, it will face the recall of a large number of measuring instruments. In order to be able to realize the on-line calibration of large-scale automated testing systems without downtime. In this paper, taking the testing branch line of low-voltage current transformer as an example, a reverse traceability method based on miniature standard is proposed, which uses a miniaturized and lightweight high-precision standard current to realize real-time online calibration of the testing system. It saves a lot of manual verification costs and greatly improves the efficiency of measurement supervision.