Electronic commerce is a new model of commerce based on the economy of network. B2B electronic com2 merce platform provides a marketplace for transactions between enterprises. In this paper , the buyers and seller’s benefit model of buyer-pull B2B electronic commerce system is established according to the principle of maximizing benefit in buyer’s market . Buyers’strategies , including setting the level of substitute , the rate of restoration and the level of subsidy , are studied to induce sellers to join the electronic commerce platform. Finally the effects of the development of technology and the economies of scale on electronic commerce are analyzed based on the model .