The invention discloses a decentration computation system based on a double-layer network. The system is constituted by a plurality of light nodes, a plurality of full nodes, and a plurality of mainnodes. A plurality of light nodes, a plurality of full nodes, and a plurality of main nodes are used to form a block chain main network, and a plurality of main nodes are used to form a main node processing network. A plurality of light nodes are used to store user specific data in the block chain network. A plurality of full nodes and a plurality of main nodes are used for a consensus mechanism to store a complete block chain. In the main node processing network, a plurality of main nodes comprise computation nodes having computation functions, which are used to carry out off-chain data computation tasks to acquire computation results. According to the technical scheme provided by the invention, a plurality of main nodes are used for resource isolation, and high expandability is provided,data processing constraints are reduced, and the data throughout of the system is effectively improved.