Background Gasdermin D (GSDMD) is well known as a downstream of inflammasomes. However, the roles of GSDMD itself in hepatocellular carcinoma (HCC) remain unclear. Methods Two independent cohorts of patients with HCC were analyzed to evaluate the pathological relevance of GSDMD/pTBK1/PD-L1. GSDMD knockout (GSDMD-/-) mice, Alb-Cre mice administered with an adeno-associated virus (AAV) vector that expressed the gasdermin-N domain (AAV9-FLEX-GSDMD-N) and their wild-type littermates were used to induce hepatocarcinogenesis or metastatic HCC. Combination of anti-programmed cell death protein-1 (PD-1) and GSDMD inhibitor dimethyl fumarate (DMF) was used to test for improved therapeutic efficacy. RNA sequencing was used to explore the mechanisms how GSDMD promoted HCC progression. Results The expression of GSDMD and GSDMD-N was upregulated in HCC tissues or metastatic HCC tissues and positive GSDMD expression indicated grim prognosis. Diethylnitrosamine/carbon tetrachloride or thioacetamide-treated GSDMD-/- mice exhibited decreased liver tumors. In contrast, AAV9-FLEX-GSDMD-N promoted hepatocarcinogenesis. RNA sequencing manifested that knockout of GSDMD impacted the cyclic GMP-AMP synthase (cGAS) pathway and immune-associated pathway. GSDMD damped cGAS activation by promoting autophagy via outputting potassium (K+) and promoted programmed death ligand-1 (PD-L1) expression by histone deacetylases/signal transducer and activator of transcription 1 (STAT1)-induced transactivation of PD-L1 via importing calcium (Ca2+). High Mobility Group Box 1/toll-like receptor 4 (TLR4)/caspase-1 pathway contributed to the overexpression and cleavage of GSDMD. Anti-PD-1 combining with DMF largely impaired HCC progression and metastasis. Conclusions Targeting GSDMD could promote expression of interferons through inactivation of cGAS pathway and downregulated the PD-L1 expression. Therefore, combined anti-PD-1 and GSDMD inhibitor might serve as an effective treatment option for patients with HCC with GSDMD upregulation.