To investigate the efficacy and safety of dexmedetomidine combined with subcutaneous morphine patient-controlled analgesia in the treatment of breakthrough cancer pain （BTcP）. Methods: 75 patients with BTcP were divided into control group (25 cases C group), morphine group (25 cases M group) and dexmedetomidine group (25 cases D group) randomly. Group C was given morphine orally to control BTcP; Group M was given morphine injected subcutaneously to control BTcP; Group D was given morphine combined with dexmedetomidine injected subcutaneously to control BTcP .The daily oral morphine equivalent (OME), background pain numerical rating scale score(NRS),NRS of BTcP, the relief time of BTcP, EORTC QLQ-C30 quality of life scale,Self-rating depression scale (SDS) and adverse reactions were investigated. Results: OME was significantly increased in three groups on the 20th day after treatment , and it was significantly increased in group C when compared with group M and group D (P 0.05). NRS of BTcP in group D was significantly decreased than that in group M and group C (P 0.05). The relief time of BTcP of group D was significantly decreased than that of group M and group C (P 0.05). The SDS of group D was significantly decreased than that of group M and group C (P 0.05). The incidence rate of adverse reactions in group D was significantly lower than those in group M and group C (P 0.05). Conclusion: Dexmedetomidine combined with morphine Patient-controlled Subcutaneous Analgesia could relieve BTcP more quickly, reduce the dosage of basic analgesics, improve the quality of life and depression, and reduce the incidence of adverse reactions, which is worthy of clinical application.