CircRNAs　have　been　reported　to　play　crucial　roles　in　tumor　progression　and　recurrence,　showing　potential　as　biomarkers　in　cancer.　However,　the　global　abundance　of　circRNA　and　their　involvement　in　hepatocellular　carcinoma　(HCC)　development　have　not　been　fully　explored.　Whole　transcriptome　sequencing　was　performed　on　tumor　and　peritumor　from　60　patients　with　HCC　to　quantify　the　expression　of　circRNAs,　and　the　global　circRNA　abundance　was　calculated　by　circRNA　index　(CRI).　Gene-set　enrichment　analysis　and　weighted　gene　co-expression　network　analysis　were　used　to　reveal　the　biological　signaling　pathways　associated　with　the　global　circRNA　abundance.　The　correlation　between　the　global　circRNA　abundance　and　the　infiltration　level　of　CD8+　T　cells　was　explored　by　immunohistochemical　assays.　Small　interfering　RNA　was　used　to　knock　down　the　pre–messenger　RNA　spliceosome　in　HCC　cell　lines　to　verify　the　regulation　of　spliceosome　in　global　circRNA　abundance.　We　found　that　dysregulation　of　global　circRNA　abundance　in　both　tumor　and　peritumor　could　lead　to　worse　prognosis.　The　immunohistochemical　assay　further　revealed　that　the　dysregulation　of　global　circRNA　abundance　in　both　tumor　and　peritumor　would　obstruct　the　CD8+　T　cells　from　invading　into　the　tumor,　which　might　explain　its　correlation　with　HCC　prognosis.　We　also　demonstrated　that　the　spliceosome　genes　were　the　main　factors　to　regulate　the　global　circRNA　abundance　in　HCC,　and　these　results　were　also　confirmed　by　knockdown　experiments.　Conclusion:　This　study　revealed　the　association　between　the　global　circRNA　abundance　and　patients＇　prognosis　and　its　underlying　mechanism.　©　2022　The　Authors.　Hepatology　Communications　published　by　Wiley　Periodicals　LLC　on　behalf　of　American　Association　for　the　Study　of　Liver　Diseases.