The invention provides a quantum secret key distributing system and method. The quantum secret key distributing system comprises a sending end and a receiving end, wherein a quantum channel and a classical channel are formed between the sending end and the receiving end; the sending end comprises a laser device, a first quantum random number generator, a signal state and decoy state encoder, a phase modulator, a second quantum random number generator, a register, a first transceiver and a first quantum secret key generator; and the receiving end comprises a first beam splitter, a second beam splitter, a translation device, a third quantum random number generator, a first detector, a second detector, a second transceiver and a second quantum secret key generator. According to the quantum secret key distributing system, the requirements of the whole system for the number of signals can be reduced, the coding rate of the system can be increased, and the transmission distance of a quantumsecret key and the generation speed of the secret key can be increased.