Service grids possess the features of intelligence and automation to compose heterogeneous resources and will be a commercial focus in network economy pattern. However, service grid business is loosely-coupled, distributed and long-running, so there is a real challenge for the researchers to provide consistency and reliability for service grid business. This paper references the transaction management methods in Web service and the safepoint concept in workflow system, combines with the feature of the service grid, and then presents a transaction management model based on service grid. This model guarantees the robustness of grid service composition and assures that service grid enabling system provides consistent and reliable results for the consumers.