The parallel data transmission based on multi-copy is a key strategy to enhance transmission speed and ensure the QoS of data grid. Currently how to select replica nodes to achieve multiple optimization objectives is an import problem to be solved. To satisfy the constraint of transmission time for service request, a model is proposed. The network load and services tolerance are all taken into account by putting forward a tolerance function for service request, taking network load and tolerance functions as optimization objective at the same time, and introducing a weighting factor to balance the two functions. In experiments various parameters of the model were detected, and good results are achieved in decision-making. It shows that the model is correct and effective.