In　the　paper,　the　characteristics　of　the　hollow-core　photonic　crystal　fiber　(PCF)　filled　with　large　thermo-optic　coefficient　liquid　were　calculated　and　analyzed　using　the　Full-vector　plane　wave　method　(FVPWM).　Two　filling　ways　were　used　to:　One　is　only　filling　the　hollow　core　of　fiber,　another　is　filling　all　the　air　holes　of　the　fiber.　The　change　of　the　PCF＇　s　effective　refractive　index　was　investigated　by　changing　the　size,　queueing　discipline,　distance　of　air　holes,　and　filling　the　air　holes　with　gas　and　liquid　etc.　The　electromagnetic　theory,　the　character　of　transmitting　light　and　the　applications　of　PCF　have　researched.