Abstract: Objective To investigate retrospective memory （RM） and prospective memory （PM） impairment in patients with mild-to-moderate cancer pain， and study the influence of cancer pain on memory. Methods Thirty-seven patients underwent mild-to-moderate cancer pain and 37 healthy controls were enrolled in this study. General cognition evaluation and questionnaires of RM and PM were performed in them. Results Compared with healthy controls，group of cancer pain had lower mini-mental state examination score （24.19±3.20 vs. 27.54±1.83， P＜0.01）， but higher PM score （14.76±4.53 vs. 9.59±1.38， P＜0.01）. RM score in group of cancer pain was lower than healthy controls， but with no significance（12.78±4.27 vs. 12.91±5.12， P＞0.05）. Conclusion Patients with mild-to-moderate cancer pain undergo cognitive impairment，especially in memory function，mainly in PM.