This article explores the mechanisms and impact of Maximal Extractable Value (MEV) in blockchain networks in detail. MEV refers to the practice of block producers manipulating transaction orders to extract additional profits, involving key participants such as miners, validators, and searchers. The article examines the transaction ordering mechanisms of different blockchains, including Ethereum, Bitcoin, and Solana, and introduces common MEV types like front-running and sandwich attacks. It also discusses MEV's effects on the DeFi ecosystem. Finally, the article proposes various solutions spanning the consensus to application layers to mitigate the negative impact of MEV on blockchain networks.