A method for providing oracle service of a blockchain network by using zero-knowledge proof includes steps of: (a) in response to feeder terminals registering data feeder transactions, including commitments generated with a commitment key and off-chain data, encrypted data generated by encrypting the off-chain data with a public key and data validation values proving with feeder zero-knowledge proof keys that the commitments are identical to the off-chain data, onto the blockchain network, the aggregator terminal acquiring at least one data feeder transaction therefrom; (b) the aggregator terminal verifying data validation values with its corresponding feeder zero-knowledge proof key, decrypting encrypted data with a private key, generating on-chain data from the decrypted data using a calculator and calculation validation values proving with an aggregator zero-knowledge proof key that the on-chain data is generated from the decrypted data, and registering the on-chain data and the calculation validation values onto the blockchain network.