The invention discloses an aluminum alloy melt purifying device. The aluminum alloy melt purifying device comprises a holding furnace and an SNIF online degassing device. The SNIF online degassing device comprises a first rotor and a second rotor which is arranged in parallel to the first rotor; the rotating speed of the first rotor is 450-600rpm, the argon flow on the first rotor is 4.5-6.0m<3>/h, the rotating speed of the second rotor is 300-450rpm, the argon flow on the second rotor is 2.8-3.2m<3>/h. According to the aluminum alloy melt purifying device disclosed by the invention, a single-rotating rotor type metal refining device of TS degassing equipment is replaced by double rotor equipment of the SNIF online degassing device, so that the contact area and the contact time of air bubbles and melts are increased to improve the degassing and purifying effect when the melts pass through the SNIF online degassing device, and furthermore, the quality of ingots is improved.