The study on new rheoforming technologies of semisolid alloys has recently been one main subject interesting many professors, experts and industrials, and so many new methods about preparing semisolid alloy slurry and rheoforming process have been put forward. The semisolid slurry of AlSi7Mg alloy was prepared by being poured at a low superheat and stirred by an electromagnetic field at a low power for a short time, and then the slurry was further soaked for proper time and finally rheoformed into a key-shaped die cavity in this paper. The influence of slurry temperature, injection specific pressure and injection speed on the rheoforming process was also studied. The experimental results show that if AlSi7Mg alloy melt is poured at 630°C or 650°C and meanwhile stirred by an electromagnetic field at a low power for a short time, the most primary α-Al grains solidified in the slurry are spherical and only a few are rosette-like. If the slurry after made is then soaked in the liquidus-solidus range for some time, the ripening of primary α-Al grains is developed further and they become more spherical and larger. The experimental results also show that the slurry temperature, injection pressure and speed have a great influence on filling ability. The higher the slurry temperature, injection pressure and speed, the higher the slurry filling ability, and the shorter the core distance from the ingate, the more easily the die cavity is filled. With the given key-shaped casting, if only the slurry temperature should be equal to or more than 585,, or the injection pressure is equal to or more than 20 MPa, or the injection speed should be equal to or more than 1.73m/s, the key-shaped die cavity can be filled completely. The microstructural distribution in the casting is very homogeneous and it shows that the slurry prepared by the new method is very suitable for rheoforming and helpful to obtaining high quality castings.