The highly pathogenic avian influenza A virus poses a global threat to human health. Avian influenza RNA polymerase protein PAC was used in the screening of two herbal plant extracts for anti-influenza agents. As a result, chlorogenic acid was identified to be PAC ligand and was discovered to inhibit polymerase activity. Hence, this work revealed a potential anti-influenza lead compound and provided an important step in the discovery of new anti-influenza drugs.