A frequency converter control circuit (10), a frequency converter and a microwave oven. The control circuit (10) comprises a rectifier circuit (11) and an inverter circuit (12), the inverter circuit (12) being connected to the rectifier circuit (11), and the inverter circuit (12) comprising a switch tube (13) and a switch circuit. The switch circuit comprises a sampling circuit (15) and a differential detection circuit (16), an input terminal (151) of the sampling circuit (15) being connected to a collector electrode (131) of the switch tube (13), so as to collect a voltage waveform of the collector electrode (131) of the switch tube (13). An input terminal (161) of the differential detection circuit (16) is connected to an output terminal (152) of the sampling circuit (15), so as to detect a real-time slope of the voltage waveform of the collector electrode (131) of the switch tube (13), and an output terminal (162) of the differential detection circuit (16) is connected to a base electrode (132) of the switch tube (13), and is used to control the conductive state of the switch tube (13) according to the real-time slope of the voltage waveform of the collector electrode (131) of the switch tube (13), thereby increasing timing precision of conduction control of a switch tube (13).