the paper showcase the synergistic effect framework and apply it to a study on electricity energy groups of internet bidding platform on B2B supply business. We enumerate electricity grid enterprise group’s purchase system. Since 2006, by setting up the multi-layer purchase system based on internet. Chinese energy enterprise group began to adopt internet supply platform and take full advantage of synergistic effect and scale effects, decrease the trade cost of whole supply chain. From the perspective of system synergy, the paper firstly analyzed the model building on e-procurement platform, and then offered a set of evaluation index on synergistic effect, lastly through empirical analysis, point out there is not only positive synergistic effect but also negative synergistic effect on the e-business platform of the purchase system.