In order to improve the reliability and economy of DER grid-connected operation, a DER monitoring system is designed based on B/S framework. To resolve the less flexibility of family-DER monitoring system, this paper designs the monitor platform, and transplants Boa server and the CGIC standard library. On these basis, the Mini SQL embedded database and Web interface are set up. The monitoring system using B/S framework can save construction cost of master station and private network, ensure DER reliability and display information in Web interface. In the end, this monitoring system is tested in Engineering Research Center for DER grid-connected. The results show that DER grid-connected operation can be monitored effectively by this monitoring system. This work is supported by National High-tech R & D Program of China (863 program) (No. 2012AA050213).