In this work, a series of novel substituted polycyclic pyridone derivatives were designed and synthesized as potent anti-influenza agents. The cytopathic effect (CPE) assay and cytotoxicity assay indicated that all of the compounds possessed potent anti-influenza virus activity and relatively low cytotoxicity; some of them inhibited the replication of influenza A virus (IAV) at picomolar concentrations. Further studies revealed that, at a concentration of 3 nM, three compounds (10a, 10d, and 10g) could significantly reduce the M2 RNA amounts and M2 protein expression of IAV and inhibit the activity of RNA-dependent RNA polymerase (RdRp). Among them, (R)-12-(5H-dibenzo[a,d][7]annulen-5-yl)-7-hydroxy-3,4,12,12a-tetrahydro-1H-[1,4]oxazino[3,4-c]pyrido[2,1-f][1,2,4]triazine-6,8-dione (10a) was found to be a promising anti-influenza drug candidate with good human liver microsomal stability, as well as with better selectivity index and oral bioavailability than Baloxavir.