Blockchain, as an emerging service architecture integrating multi-technology, has attracted extensive attention from the academia and industry due to its decentralization and immutability. However, blockchain is vulnerable to various attacks due to its complex architecture, and the increasing security incidents year by year lead to huge economic losses, which seriously hampers the development and application of blockchain technology. This work studies the architecture, principle, and defenses of existing blockchain attacks from two dimensions of hierarchical classification and attack association analysis. Firstly, the existing blockchain attacks are classified according to the hierarchical structure of the blockchain, the attack principles of these attacks are introduced, and their commonness and characteristics are analyzed. Secondly, some efficient defenses are given based on the analysis and summary of the existing solutions. Finally, this study constructs a comprehensive blockchain defense system based on several blockchain attack clusters summarized by attack association analysis, and prospects the security situation of blockchain in complex service scenarios in the future.