PCA vs Non-PCA Intravenous Hydromorphone Titration for Severe Cancer Pain

Inclusion Criteria: 1. With written informed consent signed voluntarily by patients themselves. 2. Cancer patients aged 18-70 years old. 3. Patients with cancer pain more than or equal to NRS 7 during previous 24 hours. 4. Patients who will not be treated with radiotherapy within 7 days prior to randomization and during study. 5. Patients who need chemotherapy, long term administration of hormone, targeted therapy, or bisphosphonates therapy should undergo a stable anti- tumor therapy prior to randomization. 6. Patients or his/her caregivers who are able to fill out the questionnaire forms. 7. Ability to correctly understand and cooperate with medication guidance of doctors and nurses. 8. Without a history of anaphylaxis of narcotic drugs. 9. Without psychiatric problems. 10. ECOG performance status ≤3. 11. Not participated in another drug clinical trial within one month before inclusion（including hydromorphone）. Exclusion Criteria: 1. Patients diagnosed with non-cancer pain or unexplained pain. 2. Patients suffered with post-op pain. 3. Patients having paralytic ileus. 4. Patients who have hypersensitivity to hydromorphone. 5. There are abnormal lab results, with obvious clinical significance, such as the creatinine ≥ 2 fold of upper limit of normal value, or ALT or AST ≥ 2.5 fold of upper limit of normal value (≥ 5 fold,to the patients with liver metastasis or primary liver cancer), or liver function of Child C grade. 6. Patients having a incoercible Nausea and vomiting. 7. Monoamine oxidase inhibitor (MAOI) was administrated two week before randomization. 8. Patients who are pregnant or lactating,who plans to be pregnant within one month after the trial（including male）. 9. Patients who are opioid abuse. 10. Patients who are alcohol abuse. 11. Patients who are cognitive dysfunction. 12. Patients having a severe psychotic depression. 13. Patients with any other medical condition or reason, in that investigator's opinion, makes the patient unable to participate in a clinical trial.