The purpose of this paper is to discuss spray control of nozzle for heavy duty diesel engines. This paper will focus on fuel flow analysis of nozzle, key component of FIE (Fuel Injection Equipment). The optimum designed nozzle controls fuel flow and improves flow efficiency.FIE is required to produce higher injection pressure which creates better atomization and higher utilization of air. But the higher injection pressure results in increased pump driving torque, larger pump size and higher cost.To improve the fuel flow characteristic of nozzle, we analyzed it and developed a theoretical analysis method with computer model simulation to the optimum design nozzle. We also confirmed its effect by experiments.