A control circuit and a control method for a power converter are provided. The power converter includes a plurality of resonant tanks and a plurality of switches disposed between an input terminal and an output terminal. The switches correspond to a first mode and a second mode, respectively, and the control circuit includes a first switch control circuit, a first zero current detection circuit, a second zero current detection circuit, a first switch off detector, a modulation time calculation module, a second switch control circuit, a third zero current detection circuit, a fourth zero current detection circuit, and a second switch off detector. The control circuit uses a plurality of zero current detection circuits to perform time modulations on a plurality of rectifier switches in the switches.