This invention provides a method and a terminal device for a multi-band antenna automatically tuning impedance matching, and belongs to the technical field of communication. The method includes: obtaining an operation current value and an output power value of a power amplifier upon transmitting a signal; obtaining a logical control parameter for controlling an antenna tuner based on the operation current value and the output power value, and adjusting the impedance matching of the antenna by using the logical control parameter. The efficiency for impedance matching of the antenna upon operating in the multi-bands may be improved, and the power saving can be better implemented under the condition of assuring the performance of the antenna.