Abstract: Objective To compare the efficacy and safety of intravenous injection and oral taken of morphine in the treatment of severe cancer pain.Methods 35 patients with severe cancer pain were randomly divided into oral group (n =16)and IV group (n =19).Results The time from start of treatment to achievement of CR /PR in the oral group was significantly longer than that in the IV group,and there was no significant difference of incidence rate of complications be-tween two groups.Conclusion Both oral taken and intravenous injection of morphine can effec-tively alleviate severe cancer pain,and compared with oral take,the intravenous injection of mor-phine is even more effective,so it is worthy of popularization.