Abstract: Objective To discuss the effect of intrathecal injection of morphine combined with dexmedetomidine on the analgesic effect in patients with severe cancer pain advanced colorectal cancer. Methods 112 patients with severe cancer pain advanced colorectal cancer in Chongqing Yunyang People's Hospital were selected from December 2018 to December 2019, they were randomly divided into the morphine group （n=56） and combined group （n=56）. The morphine group was treated with intrathecal injection of morphine, the combined group was treated with intrathecal injection of morphine combined with dexmedetomidine. The analgesic effect visual analog scale （VAS）, inflammatory response interleukin- 6 （IL-6）, tumor necrosis factor-α （TNF-α）, morphine dosage and adverse reactions were compared between the two groups. Results The VAS score, IL-6 and TNF-α in the morphine group and the combined group after 1 day, 3 days and 7 days of treatment were significantly lower after treatment initiated. The VAS score, IL-6, TNF-α, the daily dosage of morphine and the incidence of adverse reactions in the combined group were all significantly lower than that in the morphine group （all P<0.05）. Conclusions Intrathecal injection of morphine combined with dexmedetomidine can effectively improve the analgesic effect and inflammatory response of patients with severe cancer pain advanced colorectal cancer, and it was helpful to reduce the dosage of morphine and incidence of adverse reactions, it's worthy for further clinical promotion.