This paper proposes an Extensible Monitoring and Discovery Service for grid environment MASSIVE (MEMDS). The MASSIVE project focuses on developing a Multidisciplinary Applications-oriented Simulation and Visualization Environment. In the MEMDS, appropriate mechanisms make custom information services established and deployed easily, and the developed APIs simplify the access to the MDS and provide a uniform interface for programmers. Corresponding practices show that the MEMDS improves the extensibility and flexibility of the grid information service.