Background: 1. Biliary tract cancer (BTC) accounts for 4% of all digestive tract cancers. In 2016-2020, the incidence of BTC has gradually increased worldwide. In China, gallbladder carcinoma accounted for 1.7% of all tumors and 1.9% of deaths in some regions. 2. The standard second-line treatment regimen is mFOLFOX, with an ORR of 5%, PFS of 2 months and OS of 6.2 months. Methods: This is a single-arm, open-label, phase Ⅱ study, approximately 31 patients of unresectable locally advanced or metastatic BTC with HER2 overexpression will be enrolled. Each treatment cycle is 14 days. Therapeutic regimen: Disitamab Vedotin 2.5mg/kg IV, D1, Q2W + Zimberelimab 240mg IV, D1, Q2W All patients treated until a loss of clinical benefit or unacceptable toxicity is observed by the investigator. Objective: to evaluate the efficacy and safety of Disitamab Vedotin + Zimberelima in patients with unresectable locally advanced or metastatic BTC with HER2 overexpression Disitamab Vedotin: Vedecitumab is an antibody-drug conjugate (ADC), with a humanized antibody conjugated to four tubulin inhibitor molecules (DAR=4) Zimberelimab: Zimberelimab is a fully human IgG4 monoclonal antibody that specifically binds to PD-1 molecules on the surface of lymphocytes. This drug is approved for r/r cHL and is also effective in the cervical cancer. Clinical trial information: NCT05540483.