The invention discloses an acid washing system and an acid washing method for a double-metal composite pipe and belongs to the field of acid washing of pipelines. The system comprises a plurality of acid washing devices, supporting devices, detecting arms, an acidic liquid supplying device and a sucking device. In each acid washing device, a guide pipe is arranged at the upper end of a sleeve and extends into the sleeve; a nozzle is arranged at the end part of the guide pipe; shielding rings are arranged at the lower end of the sleeve; a sucking pipe, a first fixing bracket and a fastening part are all arranged on the sidewall of the sleeve; the sucking pipe communicates with an inner chamber of the sleeve; the fastening part is used for adjusting the distance from the nozzle to the inner wall of a stainless steel liner pipe; the detecting arms are fixed inside the stainless steel liner pipe through a plurality of supporting devices; the acid washing devices are fixed on the detecting arms; a plurality of shielding rings can surround the inner wall of the stainless steel liner pipe in a circle in a contact manner; the detecting arms are capable of driving the supporting devices and the acid washing devices to move axially along the stainless steel liner pipe; the acidic liquid supplying device communicates with the guide pipe; the sucking device communicates with the sucking pipe. The system can be used for realizing effective acid washing of the inner wall of the stainless steel liner pipe without causing corrosion, so the service life of the double-metal composite pipe can be guaranteed.