Currently there is no practical standard for grid middleware, most of the grid platforms are built by their own, and it’s not easy to interoperate these grid platforms. Information service is one of the key components of the service oriented grid system, and information service interoperation among heterogeneous grids is the first step towards grid interoperation. Existing grid interoperability projects mainly focus on immediate bridge mechanisms, which is intricate and of poor scalability. To address the issues, a uniform information service interoperation framework (UISIF) is proposed in the paper, which is based on the idea of mediated bridge mechanisms, and adopts virtual layer and plug-in technology. There are two well-established grid systems in China, ChinaGrid and China National Grid, and they are built with two different grid middleware, CGSP and VEGA. With UISIF, these two grid systems make information service interoperation a reality without changing the codes of current grid systems. The experiments also show that the information service interoperation has low information querying latency and high accuracy; Moreover, UISIF has good scalability based on hierarchical architecture, virtual layer and plug-in technology.