The purpose of the present study is to optimize the diesel engine injector. Discharge of many cavitation bubbles and high injection velocity were set up for the design purpose. Injector optimization was progressed through computational fluid dynamics (CFD) and the design of the experiment was used to study the interior of the injector. ANSYS CFX 13.0 was used as the CFD tool to perform the CFD analysis of 16 experimental cases; these include four cases of each design variable; the hole diameter, the hole length, the hole angle, and the K factor. The results of the analysis show that the largest impact on the cavitation comes from the K factor, and the injection velocity dominantly depends on the hole diameter. The optimum injector derived based on these results has the size of 2, 4, 4, and 4 levels, respectively, for the hole diameter, the hole length, the hole angle, and the K factor. For the injection velocity of 460 m/s, it gives the best performance when 36% volume fraction of cavitation bubbles are injected.