A preparation method for aluminum alloy semi-solid slurry induced and impregnated by a modificator comprises the following steps that (1) an Al-Si-Cu alloy ingot is placed into a graphite crucible to be subjected to fusion, refining and slag removal; (2) small pieces of Al-Sr intermediate alloy are added into the fondant, the mass fraction of Sr in the Al-Sr intermediate alloy is 9 wt.%-11 wt.%, and the mass fraction of the Sr in the fondant is 0.01 wt.%-0.09 wt.%; (3) the temperature is increased to 760-770 DEG C, heat preservation is conducted for 15-20 min, then a preheated ultrasonic amplitude-change pole probe is placed in the fondant, ultrasounds are released intermittently, the ultrasound interval of each time is 1-2 s, the ultrasounds are released for 2.0-2.5 s each time, the power is 1.0-2.0 kw, the frequency is 20 kHz, the total ultrasound time is 3-5 min, then the temperature is decreased to 585-610 DEG C, and standing and heat preservation are conducted for 8-10 min; and (4) intermittent ultrasound treatment is conducted on the fondant again, the ultrasound conditions are identical to those in the step (3), the total ultrasound time is 60-100 s, and water quenching is conducted immediately after the ultrasound treatment is completed. Grains of semi-solid structures obtained through the method are finer, rounder, more complete and more uniform in distribution and fully meet the requirements for semi-solid rheoforming, operation is easy and convenient, safety and reliability are achieved, and three-waste pollution is avoided.