The coexistence of moral hazard and adverse selection has limited the supply chain’s efficiency. A model is developed from the virtual-third party’s perspective for supply chains without core enterprises, based on the cooperation and competition among enterprises. Considering that the retailer has private information about his effort and that the manufacturer has private information about his cost, a bilateral incentive model is built to achieve both the incentive and coordination by using a quantity discount contract and AGV (d’ Aspremont and Gerard-Varet) mechanism. The result shows that three constraints (the balance, the incentive and the individual rationality constraint) could be satisfied and a steady transaction quantity in an integrated supply chain could be achieved by properly setting the parameter of profit adjustment. In other words, the contract proved in the paper can realize bilateral incentive and coordination simultaneously. At last, a numerical example is presented to assess the theory conclusions.