Objective: The objective of the study is to assess the unmet needs of cancer caregivers and to identify the possible predictors of their supportive care needs in China. Methods: This multicenter, cross-sectional study enrolled 449 cancer patients' family caregivers' dyads. Patients provided general information and Karnofsky performance status (KPS); caregivers provided general information and completed a survey of Chinese version of the Supportive Care Needs Survey-Partners and Caregivers Scale. The independent samples t-test, one-way analysis of variance, and multiple stepwise regression were used to analyze the factors that influence the needs of caregivers. Results: A proportion of caregivers who had no needs were 5.6%. A proportion of caregivers with ≥ 5 moderate or high unmet needs and with ≥ 10 moderate or high unmet needs were 77.7% and 63.2%, respectively. Healthcare services and information needs and communication and relationship needs were the most prominent areas of caregivers' unmet needs. The item "Finding out about financial support and government benefits for you and/or the person with cancer" was the highest level of unmet needs at 78.6%. The level of unmet needs was related to the patient's physical function (KPS score), caregiver's educational levels, financial burden of healthcare, as well as the level of burden related to caregiving (working status, caring for others, caregiving experience, and total caregiving time). Conclusions: The level of unmet needs of family caregivers of cancer patients in China was higher. In clinical practice, more attention should be paid to family caregivers who take care of the patient with poor physical function, those who are highly educated, faced with higher financial burden of healthcare, and are currently working, as well as those who need to take care of others, spend more time caregiving, and have no caregiving experience.