An　image　encryption　and　decryption　method　of　fractional　order　chaotic　systems　(FOCS)　with　predefined　time　synchronization　is　proposed　in　this　article.　Compared　with　the　existing　integer　order　chaotic　systems　(IOCS),　fractional　order　chaotic　systems　has　the　advantage　of　increasing　the　complexity　of　the　ciphertext.　At　the　same　time,　by　using　the　predefined　synchronization　time,　the　key　space　is　expanded,　the　complexity　of　the　key　is　increased,　and　the　security　of　the　algorithm　is　improved.　To　further　improve　the　security　of　encryption　and　decryption　process,　this　article　uses　a　combination　of　DNA　encoding,　row/column　cyclic　shift　and　XOR　diffusion,　position　scrambling　and　Arnold　scrambling.　The　simulation　tests　of　image　encryption　and　decryption　are　carried　out,　and　the　effectiveness　and　advantages　of　the　proposed　encryption/decryption　method　are　verified　by　histogram　analysis,　correlation　analysis,　entropy　analysis,　key　sensitivity　analysis　and　plaintext　sensitivity　analysis.　Copyright　©　2023　Lin,　Zhuang,　Xu,　Yang　and　Wu.