  The online Data Quality Monitoring (DQM) plays an important role in the data
taking process of HEP experiments. BESIII DQM samples data from online data
flow, reconstructs them with offline reconstruction software, and automatically
analyzes the reconstructed data with user-defined algorithms. The DQM software
is a scalable distributed system. The monitored results are gathered and
displayed in various formats, which provides the shifter with current run
information that can be used to find problems early. This paper gives an
overview of DQM system at BESIII.
