Continuous semisolid extruding extending forming process was adopted to produce LY11 alloy flat bar. The forming process, metal flow behavior in die cavity and microstructure and mechanical property of flat bar were investigated. It is shown that the LY11 alloy flat bar with transverse section of 10×50 mm and with good surface and fine equiaxed grains can be obtained by the continuous semisolid extruding extending forming process with melt pouring temperature of 770～780°C. The metal streamlines show that the semisolid slurry fills the die cavity in radiation manner and moves forward layer by layer and the velocity of slurry flow in the central area of die cavity is the maximum, and then decreases gradually from the center to side of die cavity. The tensile strength and elongation of flat bar with T6 heat treatment are 420.5 MPa and 14.2%, respectively.