The invention discloses an online detecting and state assessing 
system of a metering device. The online detecting and state assessing 
system comprises a master meter, a master meter assessing device, a data 
concentrator and a 
master station server. The data 
concentrator obtains internal collected electric quantity data of the master meter in a centralized mode and uploads the internal collected electric quantity data to the 
master station server; the master meter assessing device collects electric quantity data of a 
power grid master node in real time, reads the internal collected electric quantity data of the master meter, carries out the data statistics and comparison analysis, conducts online detection and state assessment on the master meter, and gives an alarm for the 
system abnormal situation; the 
master station server carries out remote monitoring and state assessing on the master meter. The system is low in cost, convenient to install, easy to operate and maintain, and capable of online detecting the 
voltage, the current, the power, the electric quantity and other data of the metering device, the real-time online error detecting and alarming, the secondary 
voltage drop testing, the secondary current and 
voltage load testing on the master meter are achieved, and an existing manual patrolling mode is replaced.