With the trend for smart maintenance for the Electric Multiple Unit (EMU), there is a critical need for cross-organizational data sharing. In maintenance field, blockchain technology has been introduced to enable trust among multiple stakeholders. However, the current blockchain solutions for data sharing are solely based on public chain or consortium chain, which may have the limitation of low transaction processing rate. Moreover, multiple levels of decentralization are required in cross-organizational data sharing for EMU maintenance. For the purpose of providing multiple types of ledger's governance and a performance improvement, this paper presents a method for developing EMU maintenance data sharing solution based on double blockchain. The method is validated using a case study at Shanghai EMU Depot. The proposed solution adopts Practical Byzantine Fault Tolerance (PBFT) as consensus mechanism. Interplanetary File System (IPFS) is introduced to reduce the payload of big data storage.