The invention discloses a decentralized distributed control system (DCS) and a control method thereof. The decentralized DCS comprises a field layer, a control layer, a control network and a monitoring layer; the control layer and the monitoring layer are connected through the control network; the field layer comprises to-be-monitored equipment used for generating a to-be-executed task corresponding to the to-be-monitored equipment; the control layer comprises a plurality of control units and a plurality of IO unit; the multiple control units and the multiple IO units are connected through thecontrol network; the field layer and the control layer are connected through the IO units, wherein the multiple control units and the multiple IO units are arranged independently; and the monitoringlayer comprises a plurality of servers and an operation terminal, the multiple servers comprise logic interfaces with different functions, and the operation terminal is used for generating a preset mapping table. All the control units of the decentralized DCS do not specially face the specific to-be-monitored system equipment any more, and all the control units are in a peer-to-peer deployment state and execute corresponding control functions as required.