The study aims to examine the effectiveness of virtual reality (VR) hypnosis for improving sleep in among Chinese childhood cancer survivors. Investigators will conduct a three-arm mixed-methods randomized controlled trial (RCT) among 186 Chinese Childhood Cancer Survivors (CCCs). The three groups are VR hypnosis, cognitive behavioral therapy for insomnia (CBT-I), and VR relaxation. The VR hypnosis intervention contains six 30-minute sessions conducted by a clinical psychologist on 6 consecutive Saturdays in Hong Kong Children's Hospital (HKCH) or participants' home depend on participants' preference. Instead of treatment-as-usual and sleep hygiene groups, investigators will use the CBT-I as the active control because it is recommended as a first-line treatment for poor sleep. CBT-I group will have six 30-minute sessions in HKCH or home depend on participants' preference on six consecutive Saturdays. The VR relaxation group will allow us to distinguish the effects of VR from those of VR hypnosis, which has the same length and delivery mode as VR hypnosis, but without a hypnosis component. The study will be conducted at HKCH, which is the only hospital in HK that provides medical follow-ups for children with cancer. Data collection will be done at baseline, as well as immediately and 1, 3, and 6 months after completion of the intervention. Multiple assessment timepoints will capture changes over time.