[Background] Porcine circovirus causes porcine circovirus associated disease, severe immunosuppression and clinical symptoms in pigs, causing substantial economic losses. [Objective] To study the role of porcine circovirus 3 (PCV3) capsid protein (Cap) in regulating host innate immune response, we constructed a eukaryotic plasmid expressing PCV3 protein Cap. [Methods] The expression of Cap was verified by Western blotting. The real-time quantification PCR (RT-PCR), dual luciferase gene reporting system and ELISA assay were used to study the effect of Cap on type I interferon pathway activation, and the Co-immunoprecipitation was done to study the involved antagonistic mechanism. [Results] The expression of Cap was verified, suggesting that Cap was highly expressed in the transfected cells, and Cap inhibited the activation of type I interferon signaling pathway stimulated by a synthetic DNA, poly(dA:dT). The interaction of Cap with the adaptor protein MITA of innate immune signaling pathway was identified. [Conclusion] These results indicate that Cap plays an important role in inhibiting the innate immune response of host cells by interacting with MITA. Our study provides a theoretical basis for clarification of the molecular mechanisms for PCV3-mediated immune suppression.