The semi-solid high-pressure die casting is playing an increasingly important role in the field of automotive lightweight. Herein, a numerical simulation study on the semi-solid die casting process of 319s aluminum alloy test bars was carried out. By setting different die casting process parameters for simulation calculation, the defect location, distribution, and content were analyzed in this paper. The best die casting process parameters were determined, which were with injection rate of 1 m/s and die casting temperature of 570 °C. According to the simulated defect location, the overflow system of the test bar was optimized, including the design of the overflow groove, sprue and venting channel. The semi-solid slurry was prepared by the Swirled Enthalpy Equilibration Device. Trial production of the test bar was carried out with the best die casting process parameters. The casting product is well filled and has no obvious defects. The experimental results show that the microstructure of test bar has fine and rounded grains with an average size of 28.27 μm and an average shape factor of 0.86. After T6 heat treatment, the transformation of the morphology and distribution of the strengthening phases plays a crucial role in the improvement of mechanical properties. The tensile strength increases from 269 MPa of 319s-F to 395 MPa of 319s-T6, but the elongation decreased slightly from 7.3 to 6.2 %.