As a promising direction of cryptography, the feasibility of quantum key distribution has been widely verified. However, the bottle-neck problems encountered by quantum key distribution network, such as concurrent conflict of large-scale quantum relay links, relay delay and inconvenient access to applications, are still not solved completely. In order to solve these problems, a quantum relay blockchain scheme is proposed in this paper. In the scheme, each relay node in a target network negotiates a quantum key with everyone of its adjacent nodes respectively, and calculates the XOR values of any two quantum keys from these quantum keys, then encapsulates these XOR values into a transaction. A server encapsulates all the current transactions into a block based on which real-time quantum key services can be realized. Furthermore, the scheme can be easily employed to realize quantum key service in cloud platforms with unconditional security and high efficiency. The scheme, which can be used to overcome the bottle-neck of quantum key distribution network, will play a critical role in future world-wide quantum key service.