The hair curler is composed of a handle assembly, a cylindrical metal sleeve, an external clamping assembly pivotally connected to the cylindrical metal sleeve, and a heating core assembly installed in the metal sleeve and electrically connected to the handle assembly; the width ratio of the cylindrical metal sleeve is The width of the handle assembly is small; a temperature control circuit board is arranged inside the handle assembly, and the heating core assembly is connected to the temperature control circuit board NTC temperature sensor and the heating mica board, the heat transfer mica board closely connected to the surface of the heating mica board, and the connecting heat transfer mica Plate heat transfer sheet; the heating mica plate includes a mica substrate and a heating wire wound on the mica substrate, and the heating wire is electrically connected to the temperature control circuit board; the NTC temperature sensor is located between the heat transfer sheet and the heat transfer mica plate.