Flow characteristics of nozzle significantly influence spray break up and atomization.Needle lift and pressure of nozzle was obtained in common rail(CR) and pump-line-nozzle(PLN) system.Re-sults show that the needle of the injector opens more quickly as injection pressure is increased in CR sys-tem while closing speed is hardly influenced by injection pressure.The opening and closing speeds of CR system are lower than those of the PLN system.FIRE code was used to calculate the flow characteristics of the injector in the two injection systems.Development and distribution of cavitations in the nozzle were analyzed.The calculated flow rate has good agreement with the experimental results.Cavitations of the injector are different under two injection systems.Cavitation location moves from the bottom to the top of the inlet during needle rising in the CR system.In contrast to this,cavitation location is always at the top of the inlet in the PLN system.