The year 2021 is the first year of the 14th Five-Year Plan and the Second Centenary Goal. The Outline of the 14th Five-Year Plan for Economic and Social Development and Long-Range Objectives Through the Year 2035 of the People’s Republic of China takes blockchains as one of the key industries in the digital economy，and makes clear the development directions of technical innovation and industrial application of blockchains. In 2022，the 14th Five-Year Development Plan for the Digital Economy issued by the State Council points out that the key technology innovation capacity in strategic and forward-looking fields such as blockchain should be enhanced. Under the continuous guidances of policy dividend and technology investment，blockchains have made important progresses in terms of technical innovation，technical convergence and technical application in 2021. This report provides a systematic overview of blockchain development at home and abroad in 2021，which focuses on technical innovation，technical convergence and technical application of blockchains. In respect to technical innovation of blockchains，we summarize the breakthroughs in consensus algorithm，peer-to-peer network，smart contract，cross-chain collaboration，security and privacy，and scalability. In respect to technical convergence of blockchains，we introduce the integrated situations of blockchain with Internet of Things，Cloud Computing and Articifical Intelligence. In respect to technical application of blockchains，we present the applications of blockchain in agriculture，justice，epidemic prevention，government affair，and dual carbon. By overviewing the development of blockchains in 2021，this report will provide references for those people who want to know the development of blockchains and plan the development of the digital economy.