To shorten the design period of a hydraulic system and achieve distributed cooperative design by experts, this paper proposes a model of the network collaborative design of a hydraulic system based on multi-agent technology. This model consists of three layers: the management agent layer, the middle agent layer and the resource agent layer. Its agent of the same layer adopts distributed structure, and each autonomous agent is constituted of a group of lower subordinate agents. This structure meets the need of distributed control of the cooperative design. By dynamic data exchange of agents, it carries out their communication, coordination and conflict resolution, and finally gets the global target. From the developed example, a multi-agent system can easily integrate existing engineering design tools with analysis tools. Its concurrent design process can improve design efficiency.