Abstract: The technology of Blockchain has the characteristics of decentralization, non-tampering and traceability, and it is applied to the traceability of green food, it helps to solve the quality and safety problems of Information asymmetry and untrustworthy green food. However, with the development of the network and complexity of the green food supply chain, more and more traceability information is needed. In this paper, the blockchain side chain is introduced to build a credible platform for the traceability of green food with multi-chain on the main chain. The main chain is enlarged by the side chain to improve its storage capacity, and the Bloom filter modified Bmerkle tree is used to improve the efficiency of traceability queries. Finally, the running process of traceability platform is analyzed by taking specific green food as an example. The construction of trusted main-side multi-chain traceability platform can eliminate the Information asymmetry in complex supply chain network, ensure the authenticity of traceability information, and enhance consumer confidence in green food. At the same time, it can expand the storage capacity of single chain, improve the efficiency of traceability query and protect the privacy of private data. And it is hoped to provide reference for the application of block chain technology in traceability system.