The invention discloses a direct-current heating circuit which comprises a triode, a diode, an inductor, a first capacitor, a second capacitor and a heating wire. The invention further discloses a direct-current heating electric soldering iron formed according to the direct-current heating circuit. The direct-current heating electric soldering iron comprises a soldering bit and a heating element and further comprises a ceramic tube and a thermocouple. The soldering bit is provided with a cavity, and the ceramic tube is arranged in the cavity. The heating element is arranged on the outer wall of the ceramic tube, and the thermocouple is arranged in the ceramic tube. The direct-current heating of the heating element of the electric soldering iron is achieved through the improvement of the direct-current heating circuit and the data collecting speed of a thermocouple sensor can reach the sampling rate as high as hundreds of times per second; the disturbance which causes temperature deviation is avoided; during the soldering with the soldering bit, a microcontroller unit (MCU) can quickly read temperature variations of the soldering bit and linearly improve the power of the heating wire, so that the soldering bit always maintains very low temperature fluctuation, and the welding quality is greatly improved while the welding speed of an automatic welding robot is greatly improved.