Blockchain technology,which has the advantages of decentralization and tamper-proofing,provides a new way to store information,execute transactions and handle business logic in an open environment.From the 1.0 era represented by Bitcoin to the 2.0 era represented by Ethereum,blockchain technology has revolutionized the finance,Internet of Things,supply chains and other industries.However,blockchain technology still faces many security challenges due to technical and management issues.Firstly,we discuss eight kinds of blockchain attacks in terms of information security,system security and privacy security,such as malicious information attacks,51% attacks,smart contract attacks,denial of service attacks,etc.,and analyze the principles,implementation processes and destructiveness of these attacks.Secondly,we discuss twelve blockchain security technologies from the above three perspectives,such as SmartPool,Securify analysis tool,mixing service and zero-knowledge proof,and analyze the principles,implementation processes,advantages and limitations of these technologies.Finally,we look forward into the future research directions of blockchain technology.