To be used for voltage regulator, An AC-AC direct converter with small bulk has been researched. The paper has proposed an isolated Cuk Three-Level AC-AC Converter. It is produced by applying TL AC switch unit in Isolated Cuk converter which is put forward by Slobodan Cuk. Because the two-level converter usually isn’t used in high voltage and heavy load situation, the paper proposed the cascaded type of isolated Cuk AC-AC converter. Besides, the operating principle and the control strategy of isolated Cuk Three-Level AC-AC Converter are investigated. Transient voltage feedback control is used in the converter and principle diagram of control circuit is given. By experiment results, the correctness of operating principle and control strategy of isolated Cuk Three-Level AC-AC Converter have been proved.