This study aims to translate the English version of the 'caring ability of family caregivers of patients with cancer scale (CAFCPCS)' into Chinese and validate its psychometric properties in the family caregivers of elderly patients with cancer. A methodological study. Based on the Brislin translation model, the original scale will be translated and back-translated, the Delphi expert consultation method will be adopted for cross-cultural adaptation, and the pilot will be carried out in 20-30 family caregivers of elderly patients with cancer. Then, a dual-centre prospective study will be conducted by recruiting 371-542 family caregivers of elderly patients with cancer to validate the psychometric properties of the Chinese version of CAFCPCS. The scale's content validity will be evaluated using the Delphi expert inquiry method, and the face validity will be evaluated using a pre-experiment. Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) will be used to assess structural validity, while internal consistency reliability and split-half reliability will be used to assess reliability. Public involvement is of great significance for this study. Participants will be used in a pre-test to give feedback on whether the contents of the clinical pilot version of CAFCPCS after expert consultation can reflect real problems and whether the sentences can be well understood. Based on their opinions, the research group will further refine the scale.