The invention discloses a probe heating circuit of a fast body temperature measuring device, which comprises a heating unit, a switch circuit, a processor and a heating energy control module, wherein the heating unit and the switch circuit are connected in series between a heating power supply and the ground, a PWM control signal which is output by a response processor and a control signal which is output by a heating energy control module are only used when the PWM control signal and the heating energy control module output control signals are simultaneously valid, a current loop which is flown through the heating units is communicated after the control signals are effectively conducted, thereby energy which is provided for the heating channel is controlled, the heating unit can not be overheated, and the safety of the heating circuit is improved.