Cooperation is considered to be very important for the negotiation among autonomous agents in a multi-agent system (MAS). Papers on cooperation and negotiation in MAS have provided a variety of approaches. However, the case of cooperation and negotiation in dealing with real-world problems with many complicated restrictions has not been thoroughly examined. In this paper, a Cooperative Negotiation Strategy (CNS) is proposed for solving real-world problems such as the Loading, Allocating and Scheduling Problem (LASP). CNS is based on the idea of Drum-Buffer-Rope (DBR) in the Theory of Constraints (TOC), heuristic algorithms, and the knowledge of skilled workers in the real world. Experimental results show that the proposed CNS is valid for relaxing the conflicts among agents and excluding deadlock states.