Method and device for writing service data in block chain system

A method for writing transaction data in a blockchain system is disclosed. The blockchain system comprises at least one blockchain. The method comprises: receiving a blockchain transaction data writing request comprising transaction feature information of transaction data to be added to the blockchain; determining a blockchain matching the transaction data to be added to the blockchain according to a blockchain data record table and the transaction feature information of the transaction data to be added to the blockchain, wherein the blockchain data record table records transaction type identification information associated with the blockchain for reflecting transaction feature information of transaction data in the blockchain; and writing an execution result of the transaction data to be added to the blockchain into the blockchain matching the transaction data to be added to the blockchain.