The invention discloses an automatic tin adding electric soldering iron which comprises a transmission module and a heating module. The transmission module comprises a shell, an inner cavity, an inner ceramic cavity, a pushing body and a wire adding button, wherein the upper end of the inner ceramic cavity is sleeved with the pushing body. A pair of one-way rotation circular gears are arranged at the joint of the inner cavity and the inner ceramic cavity. The side faces of the circular gears are provided with meshed straight gears. The lower ends of the straight gears are hinged to the upper end of the pushing body. A spring is arranged at the lower end of the pushing body. One side of the pushing body is in a conical shape with the large top and the small bottom. The wire adding button is hinged to the shell. The wire adding button can just press the conical side of the pushing body when rotating so that the pushing body is made to move upwards. The heating module comprises a heating body with the lower sharp nozzle type end, a conductor winding wire, a heating wire and a control circuit board, the upper end of the heating body is connected with the shell, the conductor winding wire is arranged at the lower portion of the inner ceramic cavity, and the lower portion of the inner ceramic cavity stretches into the heating body till the tip nozzle position, a user can operate the automatic tin adding electric soldering iron with one hand, tin wires are molten during welding, and no dead tin is generated.