Quantum key distribution (QKD)^1,2 has the potential to enable secure communication and information transfer³. In the laboratory, the feasibility of point-to-point QKD is evident from the early proof-of-concept demonstration in the laboratory over 32 centimetres⁴; this distance was later extended to the 100-kilometre scale^5,6 with decoy-state QKD and more recently to the 500-kilometre scale^7,8,9,10 with measurement-device-independent QKD. Several small-scale QKD networks have also been tested outside the laboratory^11,12,13,14. However, a global QKD network requires a practically (not just theoretically) secure and reliable QKD network that can be used by a large number of users distributed over a wide area¹⁵. Quantum repeaters^16,17 could in principle provide a viable option for such a global network, but they cannot be deployed using current technology¹⁸. Here we demonstrate an integrated space-to-ground quantum communication network that combines a large-scale fibre network of more than 700 fibre QKD links and two high-speed satellite-to-ground free-space QKD links. Using a trusted relay structure, the fibre network on the ground covers more than 2,000 kilometres, provides practical security against the imperfections of realistic devices, and maintains long-term reliability and stability. The satellite-to-ground QKD achieves an average secret-key rate of 47.8 kilobits per second for a typical satellite pass—more than 40 times higher than achieved previously. Moreover, its channel loss is comparable to that between a geostationary satellite and the ground, making the construction of more versatile and ultralong quantum links via geosynchronous satellites feasible. Finally, by integrating the fibre and free-space QKD links, the QKD network is extended to a remote node more than 2,600 kilometres away, enabling any user in the network to communicate with any other, up to a total distance of 4,600 kilometres.

量子密钥分发 (QKD) ^1,2具有实现安全通信和信息传输³的潜力。在实验室中，点对点 QKD 的可行性从实验室超过 32 厘米⁴的早期概念验证演示可见一斑；这个距离后来扩展到 100 公里范围^5,6与诱饵状态 QKD，最近扩展到 500 公里范围^7,8,9,10与测量设备无关的 QKD。几个小规模的 QKD 网络也在实验室外进行了测试^11,12,13,14. 然而，全球 QKD 网络需要一个实际上（不仅仅是理论上）安全可靠的 QKD 网络，供分布在广阔区域的大量用户使用¹⁵。量子中继器^16,17原则上可为此类全球网络提供可行的选择，但无法使用当前技术进行部署¹⁸. 在这里，我们展示了一个集成的空对地量子通信网络，它结合了一个由 700 多个光纤 QKD 链路和两个高速星对地自由空间 QKD 链路组成的大规模光纤网络。地面光纤网络采用可信中继结构，覆盖2000多公里，针对现实设备的缺陷提供实用的安全保障，并保持长期的可靠性和稳定性。对于典型的卫星通过，星对地 QKD 的平均密钥速率达到每秒 47.8 kb——比以前高出 40 多倍。此外，其信道损耗与地球静止卫星与地面之间的信道损耗相当，使得通过地球同步卫星构建更通用、超长的量子链路成为可能。最后，