This article is aiming at solving an allocation-decision problem of lot-sizing outsourcing orders between core enterprises and multiple cooperative suppliers in service-oriented manufacturing. A one-to-many cooperative stackelberg-game model which is a double-layer framework is proposed in order to obtain an optimal price and delivery time. The upper level dynamic stackelberg sub-game is designed for decision optimization problems of lot-sizing outsourcing orders between an upper level core enterprise and a lower level suppliers’ alliance. The lower level static sub-game is designed for obtaining maximum benefit of the suppliers’ alliance from lot-sizing outsourcing orders. In the game model, the leader is the core enterprise, and the follower is the suppliers’ alliance. Moreover, cost and profit are, respectively, mapping to their revenue functions. A two-level nested solution algorithm using genetic algorithm is proposed to solve the game model. Then, an equilibrium solution of this one-to-many stackelberg-game model is acquired. The analytic hierarchy process method based on contribution degree of each supplier is used for allocating profit reasonably. Finally, an example of lot-sizing outsourcing orders of gear parts validates the feasibility of the game model and its resolving algorithm. The results prove rationality of the proposed game model and correctness of the algorithm.