In this paper, we address the design and implementation of DOVE-G (Distributed Object-oriented Virtual Computing Environment on Grid). DOVE-G is designed to integrate application and Grid services by encapsulating not only application modules but also Grid services as DOVE-G objects, and hence supports an enriched parallel programming environment on Grid by enabling users to build a parallel program as a collection of concurrent DOVE-G objects. DOVE-G is built as a multilayered runtime system which can support a unified programming view for application and Grid services. Each layer of DOVE-G is implemented in C++ class library, and interacts with one another using the interfaces in the class library to provide system modularity and extensibility.