The invention relates to a temperature control circuit for a hot knife mechanism, comprising a common-mode choke coil, a DC/DC power module, a MOS tube, an MCU, a voltage and current sampling circuit, an open-collector NAND gate, and an electric heating element. The input end of the common-mode choke coil is used for connecting a bus of an external power supply, and the output end is connected with the input end of the DC/DC power module. The positive output end of the DC/DC power module is connected with the drain of the MOS tube. The gate of the MOS tube is connected with the MCU. The electric heating element is connected between the source of the MOS tube and the negative output end of the DC/DC power module. The negative output end of the DC/DC power module is connected with the MCU through the voltage and current sampling circuit. The MCU is connected with a principal computer through the open-collector NAND gate. The temperature of the electric heating element is controlled through a closed-loop control algorithm according to the linear proportion relationship between resistance and temperature. According to the invention, a hot wire blade works in a constant-power mode, the resistance of the hot wire blade is controlled by adjusting the voltage and current of the hot wire blade, and therefore, the temperature of the hot wide blade is controlled.