Cancer pain is a common complication in the middle and late stages of cancer. According to the World Health Organization, there are about 7 million new cancer patients worldwide every year, 30~50% of which are accompanied by different degrees of pain. The findings in China are similar, with 51.1% of cancer patients with different degrees of pain in general hospitals and specialized hospitals. Since the promotion of the World Health Organization’s three-step pain relief therapy for cancer pain, the control of cancer pain has been greatly improved, and 90-97% of cancer pain patients can be pain-free with the current treatment method. There are many treatment methods for cancer pain, such as radiotherapy for tumor itself, osteoclast activity inhibitor to inhibit bone destruction, and isotope internal irradiation, etc. However, as far as the main measure is concerned, it is still oral pain medication, specifically, the three-step pain relief therapy for cancer pain.