The present disclosure relates to a quantum key distribution (QKD) method based on a tree QKD network. The method includes: judging a position of a parent node of the source node S0 and a position of a parent node of the destination node Sd; if the parent node is a trusted relay node, directly transferring an initial shared key of the source node S0 and the parent node to the destination node Sd according to an exclusive OR (XOR) relay scheme, and ending the process; and if the parent node is an untrusted relay node, emitting, by the source node S0 and the destination node Sd, photons to a measuring-device-independent quantum key distribution (MDI-QKD) receiver of the parent node through a QKD emitter, generating a shared key by an MDI-QKD method, then transmitting the shared key according to the XOR relay scheme, and ending the process.