The invention relates to a semi-solid fluidized molding method and a device for metal parts. Liquid metal with the temperature from 0 to 40 DEG C above liquid phase is guided into a pulp container, and then an ultrasonic radiation is lowered down to 1 to 30mm above the liquid surface, ultrasonic radiation is started, and the slurry is cooled at the speed ranging from 0.1 DEG C per second to 3 DEG C per second. The ultrasonic radiation can be pulse radiation or non-radiation pulse with ultrasonic frequency ranging from 12kHz to 80kHz, radiation volume power 5W / cm<3> to 100W / cm<3>, and radiation time from 15s to 1000s; the slurry is poured into molding equipment to be molded into parts after the radiation. The molded part has dense organization, fine and equally distributed grains. The device of the invention comprises a pulp container, a thermostat, an ultrasonic generation and a control unit, a sleeve, and a mold and an injection rod and a molding device. The fluidized molding method and device can be used for fluidized molding of various alloy parts made from aluminum, magnesium, tin, copper and iron etc. The method has the advantages of non-contaminated pulp, long service life of ultrasonic equipment and high part production efficiency.