The invention discloses a constant temperature electric soldering iron heating circuit which comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first diode, a second diode, a third diode, a fourth diode, double-direction controllable silicon, a first capacitor, a second capacitor, a first adjustable resistor, a second adjustable resistor, a first comparator, a second comparator, a thermocouple and a thermal resistance wire. The constant temperature electric soldering iron heating circuit is simple in structure and low in cost while guaranteeing constant temperature accurately in real time.