Abstract: This paper presents Conflux, a scalable and decentralized blockchain system with high throughput and fast confirmation. Conflux operates with a novel consensus protocol which optimistically processes concurrent blocks without discarding any as forks and adaptively assigns weights to blocks based on their topologies in the Conflux ledger structure (called Tree-Graph). The adaptive weight mechanism enables Conflux to detect and thwart liveness attack by automatically switching between an optimistic strategy for fast confirmation in normal scenarios and a conservative strategy to ensure consensus progress during liveness attacks. We evaluated Conflux on Amazon EC2 clusters with up to 12k full nodes. The consensus protocol of Conflux achieves a block throughput of 9.6Mbps with 20Mbps network bandwidth limit per node. On a combined workload of payment transactions and Ethereum history transactions, the end-to-end system of Conflux achieves the throughput of up to 3480 transactions per second while confirming transactions under one minute.