Uncertainty cost of the sellers is a big challenge the buyer (the government) encounters in public procurement setting. An implementation framework of an e-procurement system integrating multi-round negotiation and multi-attribute auction is proposed to help the buyer deal with the problem. A negotiation procedure is firstly introduced to make the sellers reveal their cost information little by little. Then the sellers with lower cost are screened out to participate in the subsequent multi-attribute auction. The research shows that the procurement mechanism is optimal from the perspective of not only the social surplus but also the buyer’s payoff.