The invention relates to a quantum key distribution method and system based on a ring QKD network, and the method comprises the steps: enabling an untrusted node to serve as an MDI-QKD detector to generate a key in the ring network when there is the untrusted relay node which appears discontinuously in a transmission path, and carrying out the transmission of a shared key through an XOR relay method. According to the invention, quantum key distribution of the ring network between any two points in a trusted relay and non-trusted relay coexistence scene can be realized, compared with a trustedrelay technology, the security is improved, and compared with MDI-QKD, the distance limitation is broken.