Objective To explore the predictive effect of brain tumor patients and primary caregivers on their financial toxicity, and to provide evidence basis for clinical intervention. Methods A total of 233 pairs of brain tumor patients and their primary caregivers were conve-niently selected as the study subjects. The patients with brain tumor and their primary caregivers were investigated 3 days after diagnosis and 6 months after diagnosis using a general situation questionnaire, the Family Adaptability and Cohesion Evaluation Scale, Comprehensive Scores for Financial Toxicity based on the Patient-Reported Outcome Measures, and the Comprehensive Scores for Financial Toxicity based on the Caregiver-Reported Outcome Measures. Based on the longitudinal actor-partner interdependence model, the prediction effect of family functioning of brain tumor patients and primary caregivers on their financial toxicity was analyzed. Results The total score of family functioning of brain tumor patients was 65(55,71) points. The total score of primary caregivers was 68(61,72) points. The total score of financial toxicity of brain tumor patients was 23(18,27) points. The total score of primary caregivers was 21 (16,27) points. From the perspective of actor effects, the family functioning of brain tumor patients and their primary caregivers had a significant predictive effect on their own financial toxicity (β=0.346 and 0.510, both P<0.05); From the perspective of partner effects, only the family functioning of the primary caregivers had a significant predictive effect on the financial toxicity of patients（β=0.372,P<0.05). Conclusion The financial toxicity of patients with brain tumor is affected by the perceived family functioning of themselves and their primary caregivers. It suggests that medical staff should pay attention to the evaluation of family functioning in brain tumor care and actively explore intervention programs focusing on family functioning.