Deduplication can be used as a data redundancy removal method that has been constructed to save system storage resources through redundant data reduction in cloud storage. Now a day, deduplication techniques are increasingly exploited to cloud data centers with the growth of cloud computing techniques. Therefore, many deduplication methods were presented by many researchers to eliminate redundant data in cloud storage. For secure deduplication, previous works typically have introduced third-party auditors for the data integrity verification, but it may be suffered from data leak by the third-party auditors. And also the customary methods could not face more difficulties in big data deduplication to correctly consider the two conflicting aims of high duplicate elimination ratio and deduplication throughput. In this paper, an improved blockchain-based secure data deduplication is presented with efficient cryptographic methods to save cloud storage securely. In the proposed method, an attribute-based role key generation (ARKG) method is constructed in a hierarchical tree manner to generate a role key when the data owners upload their data to cloud service provider (CSP) and to allow authorized users to download the data. In our system, the smart contract (agreement between the data owner and CSP) is done using SHA-256 (Secure Hash Algorithm-256) to generate a tamper-proofing ledger for data integrity, in which data is protected from illegal modifications, and duplication detection is executed through hash-tag that can be formed by SHA-256. Message Locked encryption (MLE) is employed to encrypt data for data uploading by the data owners to the CSP. The experimental results show that our proposed secure deduplication scheme can give higher throughput and a low duplicate elimination ratio.