The blockchain uses cryptography, consensus algorithm, point-to-point communication and other technologies to construct a distributed trust foundation, which realizes that the data on the blockchain can be temper-proof and traceable. Blockchain technology, originated from bitcoin, is an important technological innovation in the field of fintech. It has developed rapidly in data sharing, electronic certificate, message tracing and other fields. However, the performance and scalability problems caused by large-scale node communication limit the further development and implementation of blockchain applications. Starting from the concept of blockchain basic platform, this paper elaborates the key technologies in blockchain, including cryptography and distributed ledger, consensus mechanism, smart contract and cross chain technology, points out the existing problems and bottlenecks in the development of blockchain technology. Finally, the current application fields and challenges of blockchain technology are described from the perspective of application.