A ballistic limit curve for hypervelocity impact of spherical aluminum projectiles on a single wall aluminum plate is examined using the smooth particle hydrodynamics (SPH) method. A brief description is provided about a new in-house code with an emphasis on the axi-symmetric coordinate scheme. The Benchmark Taylor bar impact test was first demonstrated as a validation of the code. Then a series of hypervelocity impact simulations was performed in axi-symmetric coordinate. The impact velocity ranged from 2 km/s to 10 km/s. The plate thickness varied from 2 mm to 8 mm. The ballistic limit results calculated are compared with predictions from empirical correlations, and the results are shown to fall within the envelope of the empirical correlation. A simple theory is developed to analyze the characteristics of ballistic limit curves. The theory provides a good insight on the hypervelocity plate impact event and is valuable for design concerns.